Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session L1: Poster Session II (4:00 pm - 6:00 pm) |
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Room: Atrium Ballroom BC |
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L1.00001: COLD ATOMS, MOLECULES AND PLASMAS II |
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L1.00002: Microwave and RF micro-traps S. Aubin, A. Ziltz We present a theoretical study of far-detuned microwave and radio-frequency (RF) micro-traps on atom chips that derive their trapping potential from the AC Zeeman effect. These traps are inherently spin-dependent and can be used to confine any alkali ground state. Furthermore, they can be used to simultaneously target qualitatively different potentials to different spin states and atomic species. RF micro-traps traps can operate at any magnetic field, thus enabling the use of magnetic Feshbach resonances to tune atom-atom interactions. Remarkably, we find that the potential roughness that frequently plagues atom chip micro-magnetic traps is strongly suppressed in RF micro-traps. These traps can also be used for RF evaporation and for producing adiabatic potentials by applying an additional near-resonant RF field. RF micro-traps are well suited for generating one-dimensional quantum gases with tunable interactions, atomtronics, and atom interferometry. [Preview Abstract] |
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L1.00003: Observation of single Cs atoms in a far detuned optical bottle beam trap Siyuan Zhang, Gang Li, Kara Maller, Mark Saffman We report on observation of single Cs atoms in a far detuned optical bottle beam (BoB) trap. The BoB is formed by crossed 532 nm vortex beams which are projected through a single lens. Ground state trapping with a lifetime of several seconds is obtained. We will discuss the prospects for quasi-magic trapping of both ground and Rydberg atoms in the BoB using additional compensation fields. [Preview Abstract] |
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L1.00004: A Dielectric Superfluid of Polar Molecules Seth Rittenhouse, Ryan Wilson, John Bohn We consider the dielectric properties of a dilute Bose-Einstein condensate composed of polarizable molecules. In the strong field regime, the dipoles are fully polarized and produce internal fields that tend to be weak compared to the external field. However, in weaker external fields this is not necessarily the case. In this work, we demonstrate, for a class of molecular species, the dielectric behavior of this system in the weak-field regime, that is, the regime in which the polarization field of the gas plays a role comparable to that of the external field. We derive a set of self-consistent equations for this system and present solutions that behave very differently than those of ordinary dipolar gases. In doing so, we motivate the exploration of this weak-field regime, i.e. the regime of the dielectric superfluid. [Preview Abstract] |
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L1.00005: Exploring strongly correlated matter with exotic atoms Mingwu Lu, Seo Ho Youn, Richard Turner, Matthew Naides, Nathaniel Burdick, Alicia Kollar, Nobie Redmon, Benjamin Lev Advances in the quantum manipulation of ultracold atomic gases are opening a new frontier in the quest to better understand strongly correlated matter. By exploiting the long-range and anisotropic character of the dipole-dipole interaction, we hope to create novel forms of quantum mesophases, states of quantum soft matter intermediate between canonical states of order and disorder. This poster presents recent advances in the laser cooling and trapping of the most magnetic atom, dysprosium, which should allow investigations of quantum liquid crystals, mesophases thought to exist in, e.g., high T$_c$ cuprate superconductors. In addition, Dy will form the key ingredient in hybrid quantum circuits as well as in novel scanning probes using atom chips. [Preview Abstract] |
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L1.00006: ABSTRACT WITHDRAWN |
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L1.00007: Decoherence of high-$\ell$ Rydberg wave packets by collisions and electrical noise B. Wyker, S. Ye, F.B. Dunning, T.J. McKinney, C.O. Reinhold, S. Yoshida, J. Burgd\"orfer Quantum revivals in very-high-$n$ ($n$~300) high-$\ell$ Rydberg wave packets generated from parent $np$ states are used to examine decoherence induced by collisions and by the application of ``colored'' noise from a random pulse generator. The origin of the decoherence is analyzed by looking at two broadening mechanisms: inhomogeneous broadening determined by the strength of the perturbation and energy diffusion whose rate is controlled by the spectral characteristics of the noise. Use of artificially synthesized noise allows the two broadening mechanisms to be tuned separately and the resulting decoherence can be systematically studied. These mechanisms also provide a key to understanding the evolution of wave packets in the presence of CO$_2$ target gas. Research supported by the NSF, the Robert A. Welch Foundation, the OBES US DoE to ORNL, and by the FWF (Austria) [Preview Abstract] |
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L1.00008: The effect of DC electric fields on nP cold Rydberg collisions Jorge Kondo, Jader Cabral, Luis Gon\c{c}alves, Luis Marcassa, Donald Booth, James Shaffer We have investigated the role of the dc Stark effect on population transfer to the nS state 100 ns after the excitation of nP Rydberg atoms in a Rb magneto-optical trap (MOT) for 32 $\le $ n $\le $ 36. The nS population was measured as a function of the principal quantum number, as a function of the dc electric field, and as a function of the nP atomic density. The time evolution of the nS population was also measured up to 10 $\mu $s after the nP+nP state excitation. The electric fields are scanned trough the Forster resonance between 0 and 12 V/cm. The experimental results are compared to a theoretical model to calculate the probability of a transfer of population between the two states, taking into account dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions as well as the dc Stark effect. We should stress that the nP case is simpler than our previous work involving nD+nD states [1], since there are fewer potential curves involved in the process.\\[4pt] [1] J S Cabral \textit{et al}., New J. Phys. \textbf{12,} 093023 (2010). [Preview Abstract] |
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L1.00009: Loading a Far-Off Resonance Trap from a $^{87}$Rb MOT Bin Jian, William van Wijngaarden Loading a far-off resonance trap (FORT) directly from a $^{87}$Rb MOT has been demonstrated. The FORT is formed by focusing a high power (20 watts) 1064 nm infrared laser into a beam waist with a diameter of 50 $\mu$m. The trap depth is about 1.4 mK that is deep enough to trap the atoms collected by a MOT. The atom number of the MOT is about $5 \times 10^7$ with a density about $10^{10}$ atoms/cm$^3$. The temperature of the MOT atom cloud is 100 $\sim$ 200 $\mu$K during the FORT loading phase. Optimizing the FORT loading is on the way. [Preview Abstract] |
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L1.00010: Towards Doppler cooling of SiO$^{+}$ Jason Hieu Van Nguyen, David Tabor, Brian Odom Extending the techniques of Doppler cooling from atoms to molecules is challenging due to the complex nature of molecular structure. ~Rotation and vibration of the molecule result in additional dark states which may require repumping, and higher order processes such as photodissociation and predissociation may terminate the cycling transition. ~We identify SiO$^{+}$ as a promising candidate for laser cooling, which differs from previous candidates in that the cycling scheme involves three electronic states. ~ Using a rate-equation approach, we model the cooling process and find that the intervening electronic state does not require additional repumping, since decay out of it is sufficiently fast. ~ We also present our current efforts towards Doppler cooling of SiO$^{+}$. [Preview Abstract] |
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L1.00011: Doppler cooling of two-level systems by frequency comb Mahmoud Ahmed, Ekaterina Ilinova, Andrei Derevianko We explore the possibility of decelerating and Doppler cooling of an ensemble of two-level atoms by a coherent train of short, non-overlapping laser pulses. We developed a simple analytical model for describing the dynamic of a two-level system interacting with the resulting frequency comb field. Supporting numerical calculations were carried out to verify the predictions of the model. We find that the effective scattering force mimics the underlying frequency comb structure. The force pattern depends strongly on the ratio of the atomic lifetime to the repetition time. For example, in the limit of short lifetimes, the frequency peaks of the optical force wash out. We derive analytical expressions for the optimal parameters of the pulse train and study compression of velocity distribution. [Preview Abstract] |
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L1.00012: Bichromatic forces for increasing the number of atoms in miniaturized traps Joshua Grossman, William Malouf, Sara DeSavage, Adam Hammett, Charles Adler, Frank Narducci The number of atoms in a magneto-optical trap (MOT) scales very strongly with the size of the trapping beams. Therefore, atom numbers in miniature atom traps are often small. Bichromatic forces may greatly exceed spontaneous emission forces. These larger forces may be exploited to compensate for the number reduction from miniaturization. To the best of our knowledge to date, the simultaneous application of bichromatic forces in multiple dimensions has not been studied. We present our work on the development of miniature magneto-optical traps using bichromatic laser forces. [Preview Abstract] |
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L1.00013: Spectroscopy of Ho atoms and optical pumping for initialization of a collectively encoded quantum register Jinlu Miao, Jake Covey, Mark Saffman We will present results on spectroscopy of the 410.5 nm cooling transition in Ho using a source based on a frequency doubled diode laser. A laser cooled Ho sample is suitable for collective encoding of a large quantum register in the 128 hyperfine ground states. We have studied hybrid optical/microwave approaches for optical pumping into a single Zeeman sublevel and will present calculations showing the feasibility of high purity state preparation as a precursor for quantum gate operations. [Preview Abstract] |
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L1.00014: Atom Trap Trace Analysis for radiokrypton and radioargon dating William Williams, Wei Jiang, Yun Sun, Kevin Bailey, Andrew Davis, Shuiming Hu, Zheng-Tian Lu, Peter Mueller, Thomas O'Connor, Roland Purtschert, Neil Sturchio Atom Trap Trace Analysis (ATTA), a MOT-based atom counting method, is used to analyze three noble gas radioisotopes ($^{81}$Kr, $^{85}$Kr, $^{39}$Ar) covering a wide range of geological ages and applications in the earth sciences. Their isotopic abundances are extremely low, in the range of 10$^{-16}$ -- 10$^{-11}$. Yet, ATTA can trap and unmistakably detect these rare isotopes one atom at a time. The system is currently limited by the excitation efficiency of the RF discharge that produces the metastable atoms (Kr* {\&} Ar*) needed for laser trapping. To further improve the MOT loading rate, we plan to replace the RF discharge with a photon excitation scheme that employs a VUV light source at 124 nm. The VUV source can be a lamp or a free electron laser. [Preview Abstract] |
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L1.00015: Control and manipulation of cold molecular ions Shiqian Ding, Dzmitry Matsukevich Due to rich level structure, long trapping time and good isolation from environment, molecular ions confined in an rf-Paul trap are attractive for precision measurements and quantum information processing. Translational degrees of freedom of the molecular ion can be sympathetically cooled by laser-cooled atomic ions confined in the same trap. However control of an internal molecular state remains a challenging problem. A frequency comb generated by a mode-locked pulsed laser offers a tool to address ro-vibrational states of molecules via simulated Raman transitions. Based on quantum logic techniques we present a scheme for preparation, manipulation, and detection of internal states of molecular ions and report progress towards its experimental implementation. [Preview Abstract] |
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L1.00016: Radio-frequency spectroscopy of pair formation in quasi-two-dimensional strongly interacting Fermi gas Yingyi Zhang, Willie Ong, Ilya Arakelyan, John Thomas We performed radio-frequency spectroscopy of a strongly interacting degenerate quasi-2D Fermi gas of Li-6 atoms trapped in a CO2 laser standing wave trap. Confinement-induced dimer formation above the 3D Feshbach resonance was investigated by comparison with the spectrum obtained in a 3D system. [Preview Abstract] |
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L1.00017: Characterization of a Degenerate Fermi Gas of $^{87}$Sr B.J. DeSalvo, M. Yan, T.C. Killian We report progress on the study of a SU(10) degenerate Fermi gas of neutral $^{87}$Sr atoms. We will describe measurements of the magnetic sublevel populations using the optical Stern-Gerlach effect and discuss prospects for utilizing an optical Feshbach resonance to modify interactions. The ability to directly measure spin population and manipulate interactions, combined with the achievement of low $T/T_F$ paves the way toward studying the rich physics predicted for this novel system. [Preview Abstract] |
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L1.00018: Towards strongly interacting fermionic potassium A.B. Bardon, N.S. Cheng, B. Braverman, L.J. LeBlanc, J.H. Thywissen A degenerate gas of fermionic atoms at its Feshbach resonance provides a clean and versatile system to study topics such as ferromagnetism, resonant superfluids, and few-body bound states. In this talk we describe progress towards strongly interacting gases of $^{40}$K in our laboratory. Our approach differs from the standard one in that we use a microfabricated magnetic trap to initiate evaporative cooling. Once optically trapped, atoms can also be manipulated using the chip as a source of strong magnetic gradients, RF fields, and microwaves. We will discuss several improvements to our apparatus, including increased laser cooling power, a dark SPOT, a pulsing sequence for the potassium dispenser, and microwave manipulation of rubidium. We will also report on our progress towards strongly interacting gases, using a Feshbach field now stabilized to 2 parts in $10^4$. [Preview Abstract] |
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L1.00019: Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas Wujie Huang, Christian Sanner, Edward J. Su, Aviv Keshet, Jonathon Gillen, Ralf Gommers, Wolfgang Ketterle Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations through the Fluctuation-Dissipation theorem. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices. [Preview Abstract] |
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L1.00020: Real-Time Dynamics of Vortex Clusters in Trapped Bose-Einstein Condensates David Hall, Emine Altuntas, Aftaab Dewan, Thomas Langin Quantum turbulence consists of intriguing phenomena intimately connected with the behavior of vortex lines in a superfluid. While much recent work has focused on superfluid helium, it has recently become possible to observe aspects of these dynamics in trapped Bose-Einstein condensates. We report here on the experimental generation, observation, and dynamics of small numbers of vortex lines in co-rotating and counter-rotating configurations. We also demonstrate that a rotating thermal cloud can be used to manipulate the vortex lines. [Preview Abstract] |
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L1.00021: New Facility to Probe Physics With Degenerate Bose and Fermi Gases Ryan Price, Daniel Campbell, Subhadeep De, Ian Spielman A new facility to produce dual species degenerate Bose and Fermi gases is under construction at JQI. The apparatus is designed to create degnerate mixtures of bosonic rubidium ($^{87}$Rb) and fermionic lithium ($^{6}$Li). At the present, the trapping of Rb has been achieved with approximately 10$^{9}$ atoms in the MOT and 10$^{7}$ atoms captured in a 1064 nm dipole trap after RF evaporation. Further optimization is currently being performed to increase atom count in the dipole trap before proceeding with BEC studies. Concurrently progress has been made in constructing the 670.9 nm laser system for cooling and trapping Li. Furthermore a saturation absorbtion spectroscopy frequency locking scheme for Li implementing fully programmable FPGA circuit is being constructed to provide versatile and programmable frequency locking control and a future configurable platform for other electronics used within the experiment. Future progress will include the creation of a Rb BEC along with novel studies of spinor physics and then the implementation of the Li system to produce the degenerate Rb-Li mixture. [Preview Abstract] |
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L1.00022: Exploring novel solitonic structures in two-component BECs JiaJia Chang, Chris Hamner, Peter Engels We experimentally study modulational instability (MI) in two distinguishable, miscible Bose-Einstein condensates (BECs). While MI is common in many immiscible nonlinear systems, its presence in our mixture is appealing in its ability to be controlled by counterflow. Confining MI to a local area of large counterflow enables the generation of solitons without the onset of global MI. We observe for the first time in matter-waves the formation of vector dark-dark solitons along with a variety of other solitons. Current and on going results will be discussed. [Preview Abstract] |
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L1.00023: Imaging theTemporal Evolution of Spin Structure in an F=1 Spinor BEC Claire Thomas, Jennie Guzman, Gyu-Boong Jo, Dan Stamper-Kurn We observe temporal evolution of ferromagnetic domains in initially unmagnetized $^{87}$Rb F=1 spinor gases cooled into the regime of quantum degeneracy. We do so by in-situ imaging of the vector magnetization profile via two novel imaging methods: spin-echo imaging and polarization contrast imaging. The spin-echo technique allows us to overcome fluctuations in the magnetic field. Polarization contrast imaging gives us sensitivity to the projection of the spin along the imaging probe axis, allowing us to image the ferromagnetic domains. This method further allows us to characterize our imaging system by applying an inhomogeneous magnetic field to our spinor condensate, creating helical spin textures. By varying the pitch of the helix, we are able to characterize our imaging system. [Preview Abstract] |
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L1.00024: Quantum Degenerate Rubidium in an All-Optical Toroidal Trap G. Edward Marti, Ryan Olf, Gabriel Dunn, Dan Stamper-Kurn Quantum degenerate gases confined in a toroidal potential show persistent currents and other transport phenomena relating to coherent, unrestricted flow around the waveguide. Vortex states are particularly interesting in such traps because multiply-charged states are topologically stable, unlike in a simply connected condensate. Much as a SQUID attains high magnetic field sensitivity, atomic configurations containing vortices may allow for accurate, absolute rotation sensing. We report on the status of our all-optical toroidal trap for Bose-condensed rubidium-87. We will discuss techniques to generate angular momentum in the condensate as well as future prospects with spinor gases and quantum degenerate lithium. [Preview Abstract] |
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L1.00025: Degenerate Quantum Gases of Strontium Simon Stellmer, Meng Khoon Tey, Mark Parigger, Rudolf Grimm, Florian Schreck The alkaline-earth elements differ significantly from the alkalis, namely by the presence of metastable triplet states, narrow optical transitions, and a decoupling of nuclear and electronic spin in the ground state. Notably, there exists a fermionic isotope of strontium with a large nuclear spin. Recent proposals use these features for novel schemes of quantum computation and for simulations of lattice spin models. These proposals require deeply degenerate and well-controlled samples of atoms in optical lattices. As a prerequisite of such studies, we have achieved Bose-Einstein condensation of bosonic isotopes of strontium, spin-polarized Fermi gases, and combinations of the two, and we will present new work on the bosonic isotopes towards the realization of quantum simulation schemes. [Preview Abstract] |
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L1.00026: Beyond the Efimov effect: an infinity of trimer states from subcritical attractive $1/{r^2}$ interactions Nicolais L. Guevara, Brett D. Esry, Yujun Wang We have investigated the spectrum of three identical bosons interacting through a pair-wise sum of two-body attractive $1/r^{2}$ potentials. We have found an infinite number of three-body bound states even when the two-body interaction does not support any dimer state. The effect we have found thus resembles the Efimov effect, but it is {\em not} the Efimov effect since no scattering length can be defined in the usual sense for an attractive $1/r^{2}$ potential. Moreover, we show that the effective three-body potential is more attractive asymptotically than the Efimov potential. When the two-body interaction is strong enough to support dimer states, a geometrically-spaced Efimov-like spectrum appears yielding an infinite sequence of three-body bound states. We have also found that three identical fermions interacting via a subcritical attractive $1/r^{2}$ potential produces an infinite number of three-body bound energies, geometrically spaced like the Efimov effect. We have thus identified a new class of three-body states distinct from those discussed before, yet possessing some of the peculiar properties of Efimov effect. [Preview Abstract] |
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L1.00027: Progress towards Direct Photoassociative Formation of Ultracold KRb Molecules in the lowest rovibronic state $X\,^1\Sigma^+, v=0, N=0$ Jayita Banerjee, David Rahmlow, Ryan Carollo, Michael Bellos, Edward Eyler, Phillip Gould, William Stwalley We report our progress on direct formation of ground-state KRb molecules with $v$=$N$=0 using the resonant coupling of the $1\,^1\Pi$ and $2\,^1\Pi$ states just below the lowest excited asymptote (4$s$(K) + 5$p_{1/2}$(Rb)) as discussed in [1]. The molecules are formed in a dual species MOT by photoassociation using a cw titanium sapphire laser and then detected by resonance-enhanced multiphoton ionization using a pulsed dye laser. As a first step, we are continuing to assign the photoassociation spectrum reported in [2] using additional information from vibrational-state-selective detection. This research is supported by the National Science Foundation and by the Air Force Office of Scientific Research.\\[4pt] [1] W. C. Stwalley \textit{et al.}, J. Phys. Chem. A \textbf{114}, 81 (2010).\\[0pt] [2] D. Wang \textit{et al.}, Eur. Phys. J. D \textbf{31}, 165 (2004). [Preview Abstract] |
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L1.00028: Mixed Cs + K trap and production of ultracold polar molecules Marin Pichler, David Hall Our recent results on simultaneous trapping of potassium and cesium atoms in a dual MOT are presented. The goal is to form ultracold polar $KCs$ molecules by photoassociation and resonant coupling. We use external cavity diode laser for photoassociation. A Labview program controls the laser scanning and data acquisition. We present our photoassociation results with trap-loss detection in single species ($Cs$) and dual species ($Cs+K$) trap. We will outline our proposal for producing deeply bound $X^{1}\Sigma^{+}$ ground state molecules, and their detection with the resonant ionization multi-photon detection scheme. We will also discuss particular properties and applications of polar $KCs$. [Preview Abstract] |
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L1.00029: Laser Assisted Ultracold Few-body Collisions Jose P. D'Incao, Chris H. Greene Two- and three-body ultracold collisional properties are studied in the presence of a laser field. Our goal is to explore the possibility of controlling atomic and molecular losses at the more complex few-body level. We also study different association schemes that can enhance our current understanding of Efimov states. A combination of the hyperspherical adiabatic representation and the Floquet formalism are utilized to study bound and scattering properties, providing further insight into the controllability of few-body systems. We hope such studies can suggest ways to develop the coherent control of ultracold few-body processes that fundamentally affect both the stability and the lifetime of condensates. This work was supported by NSF. [Preview Abstract] |
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L1.00030: Hyperfine structure of Cs$_2$ and RbCs excited molecules Nadia Bouloufa, Olivier Dulieu, Oliver Kriegelsteiner, Romain Vexiau, Anne Crubellier, Johann Georg Danzl, Hans-Christoph N\"agerl Unlike ground state alkali-metal diatomics, very little is known about the hyperfine structure of excited electronic states. We present a preliminary analysis of the expected structure of the rovibrational levels of the Cs$_2$ and RbCs excited electronic states correlated to the lowest $^2$S+$^2$P limit based on an asymptotic model for the hyperfine Hamiltonian [1]. We set up potential curves built on long-range atom-atom interaction connected to short-range ab-initio results obtained in our group. The hyperfine structure strongly depends on the projection of the total angular momentum of the molecule, and on the sum of projections of the total angular momentum of the separated atoms. The comparison with the experimental data recorded in Innsbruck [2] will be presented. The possible interaction of electronic states at short distances due to hyperfine coupling is discussed.\\[4pt] [1] D. Comparat, et al, Eur. Phys. J. D 11, 59 (2000)\\[0pt] [2] J. G. Danzl et al Faraday Disc. 142, 283 (2009) [Preview Abstract] |
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L1.00031: Ultracold Ground-State $^{87}$Rb$_2$ Formation using Nanosecond-Timescale Frequency-chirped Light J.A. Pechkis, C.E. Rogers III, J.L. Carini, P.L. Gould We present results on ultracold molecule formation using frequency-chirped pulses. The chirps, either positive or negative, sweep 1 GHz in 100 ns through a photoassociation resonance located below the $D_2$ line in $^{87}$Rb. The intensity pulses are Gaussian with a full width at half-maximum (FWHM) of 40 ns. We use resonantly-enhanced multi-photon ionization to directly detect ground-state $^{87}$Rb$_2$ formed through photoassociation by linearly frequency-chirped pulses and subsequent spontaneous decay. In particular, we measure the rates of formation ($R$) and photodestruction ($\Gamma_{\mathrm{PD}}$) for positive and negative frequency-chirped pulses, as well as for unchirped pulses. We find that unchirped pulses yield higher values of both $R$ and $\Gamma_{\mathrm{PD}}$ than those of positively-chirped pulses, whose values in turn are greater than those of negatively-chirped pulses. Our results are an important step towards coherent control of ultracold ground-state molecule formation. This work is supported by DOE. [Preview Abstract] |
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L1.00032: Numerical studies of three-body recombination in systems with many bound states Jia Wang, Jose D'Incao, Chris Greene We have performed numerical studies of three-body recombination processes for a system of three identical bosons. Our two-body model potentials are designed to support many bound states, which produce a complex set of sharp nonadiabatic avoided crossings in the three-body hyperradial adiabatic potentials at short distance. Our model thus mimics the usual difficulties of realistic systems. To overcome these numerical challenges associated with sharp avoided crossings, we use the ``slow variable discretization (SVD)'' approach in the region of small hyperradii. At larger hyperradii, where the adiabatic potentials and couplings are smooth, we use the traditional adiabatic method. Then, using the R-matrix propagation method, we solve the three-body sch\"odinger equation out to large radii and calculate the three-body recombination rate. We also explore universal aspects of recombination for large scattering lengths under more realistic scenarios. [Preview Abstract] |
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L1.00033: Phase Transitions in 1D Open Quantum Systems and Liouville-space Entropy Michael Hoening, Matthias Moos, Razmik Unanyan, Michael Fleischhauer We discuss 1D lattice fermions and bosons coupled to quasi-local reservoirs. In the steady state these systems can undergo a transition to a critical phase for certain values of the reservoir parameters [1]. For free bosons the critical transition is accompanied by a dynamical instability, for free fermions it is associated with a vanishing of the component with long-range order. We discuss the critical transition including critical exponents, purity and entanglement in free and interacting, open fermionic and bosonic systems within a mean-field approach. 1D quantum systems can be efficiently simulated if the many-body state can be written in terms of matrix product states. A good measure for this is the bi-partite von-Neumann entropy. In the case of an open system it is no longer an appropriate measure for simulability. Instead we introduce the Liouville space entropy which quantifies the resources for a representation of the density matrix in terms of tensor product operators.\\[4pt] [1] J. Eisert and T. Prosen, arxiv:1012.501 [Preview Abstract] |
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L1.00034: Wave chaos of matter waves in periodic and disorder potentials Iva Brezinova, Lee Collins, Katharina Ludwig, Barry Schneider, Joachim Burgdoerfer For the description of the dynamics of Bose-Einstein condensates (BECs) the mean-field theory plays an important role. Within the mean-field theory the BEC is treated as a matter wave propagated via the Gross-Pitaevskii equation (GPE). We show that the GPE with repulsive interactions features chaotic wave dynamics for (a)periodic and disorder potentials. Chaos manifests itself through exponential divergence of initially nearby wavefunctions and results in random local fluctuations [1]. We discuss the implications of these observations for the limits of applicability of the GPE and the properties of the underlying many-body dynamics.\\[4pt] [1] I.~Brezinova et al., arXiv:1101.4663 (2011). [Preview Abstract] |
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L1.00035: A new apparatus for studying quantum gases in optical lattices Ulrich Schneider, Lucia Duca, Tracy Li, Martin Boll, Philipp Ronzheimer, Simon Braun, Sebastian Will, Tim Rom, Michael Schreiber, Immanuel Bloch We present the design of a new apparatus targeted at the study of equilibrium and out-of-equilibrium phenomena of quantum gases in 2D and 3D optical lattices. Specifically this apparatus will allow for a study of the crossover between 2D and 3D using bosonic and fermionic gases as well as Bose-Fermi mixtures. In addition we present a new analysis of previous results concerning the Fermi-Hubbard model and will analyze possible routes for creating many-body states with long range order, including antiferromagnetically ordered states and BCS-superfluids. [Preview Abstract] |
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L1.00036: Measurement of the shadow effect in a parametrically modulated cold atomic system Ji-Hyoun Kim, Geol Moon, Yonghee Kim, Wonho Jhe We measure the shadow effect of the cold atomic system in a parametrically modulated trap. The system shows ideal mean-field type symmetry breaking transition via changing the total number of atoms. This phase transition is originated from the competition between fluctuations and the long-range interaction mediated by the photons, the shadow effect. We apply the static bias field in the direction compensating the shadow effect, then measure the strength of the shadow effect directly from the coercive field which is the strength of the bias field to restore the symmetry. We compare this result with the other one which is extracted from the position change of the atomic cloud during the phase transition and the theory. We also expect that this negative bias-field method is useful to investigate the order-reversal transition in a system response to pulse bias field. [Preview Abstract] |
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L1.00037: Non-Equilibrium Resonant Dynamics of Ultra-Cold Bosons in the Strongly Correlated Regime Chester Rubbo, Salvatore Manmana, Ana Rey We study the static and dynamical properties of strongly interacting ultra-cold bosonic atoms loaded into a 1-D optical lattice with an external linear potential in light of recent experiments performed by the Greiner group at Harvard. Onsite strong interactions generally suppress motion, but when the external field is tuned resonantly with the interaction parameter, nearest neighbor tunneling is restored. The dynamics can be explained by mapping the system to states of dipole configurations. We obtain an exact understanding of the dynamics in few-body systems and use it to describe the many-body dynamics at low fillings. We test the validity of our model by comparisons to DMRG calculations. We also propose a controllable scheme to enhance mass transport. Finally, we extend the same study to systems exhibiting longer-range interactions. [Preview Abstract] |
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L1.00038: Universality in the Disappearance of Quantum Integrals of Motion Under Perturbation Maxim Olshanii, Kurt Jacobs, Marcos Rigol, Vanja Dunjko, Harry Kennard, Vladimir Yurovsky A central question of dynamics is to what extent it preserves the initial properties of the system. Its study in classical mechanics began with the problem of the stability of the solar system, was intensified by the Fermi- Pasta-Ulam ``paradox,'' and led to the seminal Kolmogorov-Arnold-Moser (KAM) theorem, which characterized how conserved quantities cease to be conserved under a perturbation away from integrability. Here we show that for a conceptually important class of quantum systems, the disappearance of conserved quantities is described by a universal relation. The relation, numerically confirmed for several diverse systems, follows from an exactly solvable statistical model that quantitatively describes the recently proposed connection between the many-body localization and the transition from integrability to non-integrability. [Preview Abstract] |
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L1.00039: Fermionic molecule formation by ramps across Fano-Feshbach resonance Chen Zhang, Chris Greene This project is a theoretical investigation of the properties of a gas of fermionic diatomic molecules, including the formation of these molecules from bosonic $^{87}$Rb and fermionic $^{40}$K gases through magnetic field ramps across a Fano-Feshbach resonance. We have approached the problem mainly from a few-body viewpoint. This includes a numerical calculation of the magnetic field-dependent energy spectrum, time evolution of the few body system, analysis within and beyond the standard Landau-Zener model, and also an analytical calculation of the scattering process by applying frame transformation ideas for various quasi-2D geometries. Preliminary results will be shown at the meeting including comparison with experimental results. We acknowledge funding from NSF. [Preview Abstract] |
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L1.00040: Preliminary results on a new method for producing ultracold molecular ions Scott Sullivan, Wade Rellergert, Kuang Chen, Steven Schowalter, Svetlana Kotochigova, Eric Hudson We describe a new method for the production of ultracold molecular ions. This method utilizes sympathetic cooling due to the strong collisions between appropriately chosen molecular ions and laser-cooled neutral atoms to realize ultracold, internal ground-state molecular ions. In contrast to other experiments producing cold molecular ions, our proposed method efficiently cools both the internal and external molecular ion degrees of freedom. The availability of truly ultracold molecular ions will impact fields as diverse as quantum chemistry, precision measurement, and quantum information/computation. Observations of neutral-ion interactions have been made using laser-induced fluorescence of Yb ion interacting with MOT. [Preview Abstract] |
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L1.00041: Potential Roughness in Atom Chip Microwave and RF Microtraps Austin Ziltz, Seth Aubin We present the expected potential roughness of microwave and RF microtraps (u/RF trap)s due to imperfections in atom chip wires. We focus on the theory of atom chip-based u/RF microtraps (u/RF traps) and compare to DC micromagnetic traps. In our u/RF trap geometry, potential roughness is suppressed by selection rules as well as the characteristic shape of the deviations compared to equivalent micromagnetic DC chip potentials. These studies of trap roughness are part of a greater effort to establish u/RF potentials on atom chips. These potentials are inherently conservative, spin-dependent, and allow tunable atom-atom interactions via magnetic Feshbach resonances. They can be used for interferometry of trapped ultracold thermal and quantum gases, atomtronic devices as well as novel trapping and cooling techniques. The small hyperfine splitting of potassium isotopes simplifies the engineering of u/RF potentials, while also providing bosonic and fermionic species. [Preview Abstract] |
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L1.00042: Many-body interaction and non-Abelian anyonic statistics in a chiral spin liquid Haitan Xu, Jacob Taylor We propose an approach to generate many-body interactions in two dimensions from two-spin interactions. Applying this approach to the celebrated Kitaev honeycomb model, we provide a framework for experimentally realizing and manipulating non-Abelian anyons, with explicit demonstration of topological properties of the generalized Kitaev model and its robustness to sources of local error. Potential implementations of our approach with cold atoms are considered. [Preview Abstract] |
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L1.00043: Heating and losses in 2D optical lattices Aaron Reinhard, Jean-Felix Riou, Laura Adams, David Weiss We report results on the impact of heating and losses on a Bose gas trapped in 1D tubes formed by a 2D optical lattice. We present our calculations for the heating rates, loss rates, and excited transverse band populations and show that they agree well with our measurements of these quantities over a wide range of experimental parameters. Finally, we discuss the effect of these processes on the evolution of the momentum distribution of an out-of-equilibrium 1D Bose gas, with which we are studying the onset of thermalization in nearly integrable many-body quantum systems. [Preview Abstract] |
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L1.00044: Progress toward the Disordered Hubbard Model William McGehee, Stanimir Kondov, Joshua Zirbel, Brian DeMarco We report on progress towards experimentally realizing the disordered Fermi-Hubbard model using ultra-cold $^{40}$K atoms confined in a disordered optical lattice. As a first step, we have demonstrated Anderson localization of a spin-polarized gas in an optical speckle potential. We will discuss the measured effect of weak interactions on localization. In order to reach the strongly correlated limit, we will combine this disordered potential with an optical lattice to realize the disordered Fermi-Hubbard model. This approach circumvents the difficulty of theoretical analysis and direct measurements in materials. [Preview Abstract] |
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L1.00045: 3D-1D Crossover of a Spin-Imbalanced Fermi Gas Melissa Revelle, Yean-an Liao, Ann Sophie C. Rittner, Randall G. Hulet A 3D trapped spin polarized Fermi gas has been shown to phase separate into a fully paired core and a polarized shell.\footnote{G.B. Partridge \textit{et al.}, Science \textbf{311}, 503(2006); Y. Shin \textit{et al.} Phys. Rev. Lett. 97, 030401 (2006).} Motivated by a search for FFLO pairing we have obtained the phase diagram of a 1D spin-imbalanced Fermi gas confined to an array of tubes created by a 2D optical lattice. It exhibits three phases with an inverted structure compared to 3D: a partially polarized superfluid, a fully paired phase and a fully polarized phase, depending on the degree of spin polarization.\footnote{Y.A. Liao \textit{et al}., Nature \textbf{467}, 567(2010).} We investigate the transition from a 3D to 1D gas by smoothly varying the depth of our 2D optical lattice. This changes the tunneling between the 1D tubes allowing us to study how the spin density varies with inter-tube coupling. By varying the lattice depth quickly, we can also measure spin transport in a strongly interacting system. [Preview Abstract] |
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L1.00046: Progress Towards Experimental Realization of Polarization Dependent Optical Dipole Traps in the Diffraction Pattern of a Pinhole Grant Rayner, Bert Copsey, Andrew Ferdinand, Dani May, Jennifer Rushing, Glen D. Gillen, Katharina Gillen-Christandl We work towards solving the scalability problem of neutral atom quantum computing by trapping atoms in two dimensional arrays of light-polarization dependent dipole traps formed in the diffraction pattern immediately behind an array of pinholes. Our simulations show that adequate traps result from modest laser powers [1]. Adjusting the angle of the trap laser, we can controllably manipulate the location of the traps. By exploiting the polarization dependence of the trapping potential, traps can be brought together and apart [2]. This scheme constitutes a scalable addressable system that facilitates two qubit gates. We will present progress towards experimentally verifying our previous computations.\\[4pt] [1] G. D. Gillen, et al., Phys. Rev. A 73, 013409 (2006)\\[0pt] [2] K. Gillen-Christandl and B. D. Copsey, Phys. Rev. A 83, (in production) (2011) [Preview Abstract] |
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L1.00047: Progress toward realization of antiferromagnetic ordering of cold atoms in an optical lattice P.M. Duarte, R. Hart, T.L. Yang, R.G. Hulet We present progress toward the observation of antiferromagnetic (AFM) ordering of fermionic atoms in an optical lattice using Bragg scattering of light. We first laser cool $^{6}$Li atoms using the $2S_{1/2}\rightarrow 2P_{3/2}$ transition and then further cool using the $2S_{1/2}\rightarrow 3P_{3/2}$ transition to T $\sim$ 65 $\mu$K, in order to enhance loading into a far detuned optical dipole trap. After forced evaporative cooling, an incoherent spin mixture of the two lowest magnetic sublevels of the ground state is adiabatically loaded into a 3D optical lattice. By adjusting the $s$-wave scattering length and the depth of the lattice, we tune the interaction and hopping terms of the Hubbard Hamiltonian. Bragg scattering of light can be used to detect sample ordering in the Mott insulator state\footnote{T. A. Corcovilos, S. K. Baur, J. M. Hitchcock, E. J. Mueller, and R. G. Hulet, Phys. Rev. A {\bf{81}}, 013415 (2010).}, and at lower temperatures the predicted AFM state. The increased symmetry of the AFM state allows for Bragg scattering of light from the ordered spin planes, $\pm$(${\scriptstyle{^1\!/_2}\,{^1\!/_2}\,{^1\!/_2}}$), and hence unambiguous detection of the AFM state. We present our progress in detecting the Mott insulator and AFM states. [Preview Abstract] |
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L1.00048: Damping of Bloch oscillations in the presence of localized impurities Jeremy Reeves, Matthias Vogt, Bryce Gadway, Daniel Pertot, Dominik Schneble Ultracold atoms in optical lattices provide an ideal system for the study of Bloch oscillations (BOs). Recently, there has been interest in exploring the effects of disorder on the damping of BOs, e.g. by the use of bichromatic lattices or the addition of localized impurity atoms. Here, disorder and interactions may have competing effects on the damping rate. We investigate damped BOs in a quantum-degenerate two-component mixture of $^{87}$Rb atoms in a state dependent optical lattice, in which the atoms from one component are localized while the other component undergoes BOs. [Preview Abstract] |
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L1.00049: Universal analytic inelastic rate constants for three particles in a harmonic trap Edmund Meyer, Brett Esry We present a study of three particles colliding in an isotropic harmonic trap in two regimes: when the oscillator length is much greater than and much less than the two-body s-wave scattering length. Transcendental equations that determine the energy of the interacting particles in the trap are derived for both bosonic and fermionic systems. We parametrize the recombination and relaxation using a complex short-range three-body phase. Explicit analytical expressions are obtained for the behavior of the lifetime for the case where the oscillator length is the largest length scale in the system. We find that, for negative scattering lengths whose magnitude is small in comparison to the oscillator length, that the lifetime scales as $|a|^4$, in agreement with previous studies on threshold behavior~[1]. \\[4pt] [1] J.~P. D'Incao and B.~D. Esry, Phys. Rev. Lett. 94, 213201 (2005) [Preview Abstract] |
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L1.00050: Low-Entropy Mott Insulators in the Quantum Gas Microscope Philipp Preiss, Jonathan Simon, Waseem Bakr, Ruichao Ma, Eric Tai, Markus Greiner Ultracold atoms in optical lattices are a promising candidate for the simulation of condensed matter systems due to the exquisite control over interactions and geometries. Of particular interest is the study of quantum magnetic interactions with possible insights into high-temperature superconductivity. Progress in this direction has been hindered by the difficulty of extracting local observables and attaining the requisite temperatures and entropies. Here we present the experimental realization of a low-entropy Mott insulator of ultracold atoms. Using a quantum gas microscope, we project a square lattice onto a two-dimensional $^{87}$Rb BEC. Single-site resolution of the microscope allows measurements of local number statistics. We observe 15x15-site Mott insulator domains with 95(2){\%} fidelity. The low-entropy Mott insulator domains are excellent starting points for the exploration of condensed matter phenomena, including a mapping of dipole excitations onto an antiferromagnetic Ising Hamiltonian. We expect the combination of high-fidelity initialization and single-site read-out of a cold-atom system to trigger progress in the crossover between atomic and condensed matter physics. [Preview Abstract] |
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L1.00051: Optical Lattice Realization of 1D Antiferromagnetic Ising Chain Ruichao Ma, Waseem Bakr, M. Eric Tai, Philipp Preiss, Jonathan Simon, Markus Greiner Ultracold gases in optical lattices provide a novel avenue for quantum simulation of condensed matter Hamiltonians due to the exquisite control over the interaction parameters, and the availability of local and temporal probes of the dynamics. We present a recent realization of an antiferromagnetic Ising model with transverse and longitudinal fields using Rubidium 87 in a tilted 1D optical lattice, where the dipolar excitations of the Mott Insulator are mapped to spin degrees of freedom. By sweeping the tilt of the lattice, the spins transition between the paramagnetic and the antiferromagnetic phase. We observe the quantum phase transition both in situ by single-site resolved imaging using our quantum gas microscope and by density-correlation measurements. Using a spatial light modulator, we can modify the lattice topography with high resolution. This enables us to study the impact of superlattice or random disorder on the dynamics of the phase transition, as well as the dynamics of local excitations. [Preview Abstract] |
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L1.00052: Progress Towards Single-Site Imaging of a Degenerate Fermi Gas in an Optical Lattice Katherine Wooley-Brown, Florian Huber, Dylan Cotta, Max Ebner, Widagdo Setiawan, Markus Greiner We present the development of a novel apparatus to study Hubbard model physics relevant to high temperature superconductivity and other exotic phases of matter. The experiment is designed for site-resolved imaging of a degenerate fermionic lithium-6 gas in an optical lattice. This high spatial addressability should allow us to observe the onset of novel quantum phases at higher temperatures than any macroscopic properties could be measured. We work on achieving single-site resolution and high atom detection fidelity by using a two-photon ionization process. The liberated ion and electron are then recorded with separate single-channel electron multipliers, leading to high fidelity. We present the current state of the experiment. [Preview Abstract] |
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L1.00053: Signatures of quantum criticality in cold atoms and resolution of the Fermi-Hubbard model's high temperature Mott/metal crossover Kaden Hazzard, Ana Maria Rey, Richard Scalettar We present general techniques to observe and characterize quantum critical behavior in cold atoms. Quantum criticality --- behavior manifested at finite temperature near a zero temperature phase transition --- is a central concept in condensed matter physics. It provides a key example of excitations incapable of being described by the quasiparticles and is crucial to interpreting experiments on real materials. We give a prescription to use cold atoms to resolve major open questions of the field. As one example, it is important to know the spectrum of the so-called ``finite density O(2) rotor model," which could be measured by spectroscopy of bosons in optical lattices or dynamics of spinor condensates. Moreover, applying these techniques to data from numerical determinental quantum Monte Carlo calculations, we have been able to resolve the universality class of the Mott/metal crossover in the Fermi-Hubbard model at temperatures $t^2/U\ll T \ll t$, with $t$ the tunneling rate and $U$ the interaction strength. We find that the universal physics is quantitatively described by a $z=2$ dilute Fermi gas universality class, in contrast to several other proposed scenarios. This also provides a new perspective on current fermion lattice systems' observed density profiles, doublon fractions, and compressibilities. [Preview Abstract] |
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L1.00054: ATOMIC AND MOLECULAR DYNAMICS IN INTENSE LASER FIELDS |
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L1.00055: Multiple-orbital effects on high-harmonic generation of aligned CO$_{2}$ molecules Cheng Jin, Anh-Thu Le, C.D. Lin We calculated the modulated high-harmonic generation (HHG) spectra of transiently aligned CO$_{2}$ molecules in an intense infrared laser field. The effect of interference between HOMO and HOMO-2 orbitals and the effect of macroscopic propagation of the harmonics in the gas medium are both included. The calculated results show that the minimum in the HHG spectra shifts with laser intensity which is consistent with experimental measurements. The exact position of the minimum, however, is easily influenced by the degree of molecular alignment and, through macroscopic propagation, by other detailed experimental conditions. From the HHG spectra the relative ionization probability between HOMO and HOMO-2 in different intensity region can also be estimated. In contrast to N$_{2}$ molecules, HOMO interferes with HOMO-2 only at small pump-probe angles for CO$_{2}$ molecules, and HOMO is dominant at large pump-probe angles. This study provides the needed theoretical basis for understanding how the HHG spectra can be influenced by the molecular structure. [Preview Abstract] |
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L1.00056: Medium propagation effects on high harmonic generation of Ar in a two-color laser field Guoli Wang, Cheng Jin, C.D. Lin We calculated the macroscopic HHG spectra of Ar in a two-color laser field where the single-atom response was evaluated using the quantitative rescattering (QRS) theory. The effect of macroscopic propagation in the medium on the dispersion and the Kerr nonlinearity of the fundamental laser field, and on the dispersion and absorption of the harmonics, has been analyzed. Despite that the HHG spectra exhibit different features with the change of experimental conditions, the Cooper minimum of Ar at photon energy of around 50 eV always appears. According to the QRS theory, we can extract ``macroscopic wave packet'' from the calculated HHG spectra, which only depends on the laser properties. The result also provides a basis for extracting the target structure from measured HHG spectra using a two-color laser field. [Preview Abstract] |
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L1.00057: High-Order Harmonic Generation of Homonuclear and Heteronuclear Diatomic Molecules: Exploration of Multiple Orbital Contributions John Heslar, Dmitry A. Telnov, Shih-I Chu We extend the\textit{ self-interaction-free} time-dependent density functional theory (TDDFT) approach with proper asymptotic long-range potential for nonperturbative treatment of high-order harmonic generation (HHG) of diatomic molecules. A time-dependent two-center generalized pseudospectral method in prolate spheroidal coordinate system is used for accurate and efficient treatment of the TDDFT equations in space and time. The theory is applied to a detailed \textit{all-electron} nonperturbative investigation of HHG processes of homonuclear (N$_{2}$ and F$_{2})$ and heteronuclear (CO, BF, and HF) molecules in intense ultrashort laser pulses with the emphasis on the role of multiple molecular orbitals (MOs). The results reveal intriguing and substantially different nonlinear optical response behaviors for homonuclear and heteronuclear molecules. In particular, we found that the HHG spectrum for homonuclear molecules features a destructive interference of MO contributions while heteronuclear molecules show mostly constructive interference of orbital contributions. [Preview Abstract] |
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L1.00058: A Mechanism for Isolated Attosecond Pulse Generation by Optimizing the Laser Field Peng-Cheng Li, I.-Lin Liu, Shih-I. Chu We present an isolated sub-40 attosecond generation when a hydrogen atom exposed to the optimized two-color laser field. By solving the time-dependent Schr\"odinger equation, we found that the optimized laser pulse shape can delay the electron emission time, leading to a relatively short emission duration for long-trajectory electrons and a relatively long emission duration for short trajectory electrons near the cutoff region. As a result, an isolated 35 attosecond pulse with a bandwidth of 93 eV is obtained directly from the supercontinuum of the high-order harmonic generation (HHG) due to the contribution of long trajectory. To better understand the physical origin of the attosecond pulse emission, we analyze the wavelet time-frequency characteristics of the HHG. Detailed results will be presented. This work was partially supported by DOE and NSF and by MOE-NTU-Taiwan. [Preview Abstract] |
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L1.00059: Comparison of the strong field ionization of N$_2$ and F$_2$: A TDDFT study Xi Chu, Melissa McIntyre We compare strong field ionization probabilities of N$_2$ and F$_2$ molecules using time-dependent density functional theory (TDDFT) calculations. Accurate nuclear potentials and ground vibrational wave functions are incorporated into our study. For both molecules, the effect of molecular vibration is small, while that of the molecular orientation is significant. When compared to the ionization probability of a molecule at the equilibrium geometry, we estimate the effect of the ground state vibration to be within 3\% for N$_2$ and within 6\% for F$_2$, in the intensity range from 1 to $5\times 10^{14}$ W/cm$^2$. The molecular orientation dependent ionization probabilities for both molecules at various intensities are presented. They are strongly dependent on the laser intensity, and the anisotropy diminishes when the laser intensity is high. For laser intensities of 1.6 and 2.2 $\times 10^{14}$ W/cm$^2$ we find ionization probability ratios of 5.9 and 4.3, respectively, for the parallel versus perpendicular orientation of N$_2$. This is reasonably consistent with experimental measurements [1,2] For randomly oriented molecules, the ratio of the probabilities for N$_2$ and F$_2$ increases from about 1 at $10^{14}$ W/cm$^2$ to 2 at $4\times 10^{14}$ W/cm$^2$, which agrees well with experimental results [3]. [1] I. V. Litvinyuk {\it et al.}, Phys. Rev. Lett. {\bf{90}}, 233003 (2003). [2] D. Pavicic {\it et al.}, Phys. Rev. Lett. {\bf{98}}, 243001 (2007). [3] M. J. DeWitt {\it et al.}, Phys. Rev. Lett. {\bf{87}}, 153001 (2001). [Preview Abstract] |
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L1.00060: Nonlinear atomic response to intense, ultrashort x rays Gilles Doumy, Sang-Kil Son, Christoph Roedig, Cosmin Ioan Blaga, Anthony DiChiara, Robin Santra, Marc Messerschmidt, Christoph Bostedt, John Bozek, Philip Bucksbaum, James Cryan, James Mike Glownia, Shambhu Ghimire, Li Fang, Matthias Hoener, Nora Berrah, Elliot Kanter, Bertold Kraessig, David Reis, Nina Rohringer, Linda Young, Pierre Agostini, Louis DiMauro The nonlinear absorption mechanisms of neon atoms to intense, femtosecond \textit{kilovolt} x rays are investigated. The production of Ne$^{9+}$ is observed at x-ray frequencies below the Ne$^{8+}$, 1$s^2$ absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the 2-photon ionization of Ne$^{8+}$ ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time-scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross-section is orders of magnitude higher than expected from previous calculations. [Preview Abstract] |
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L1.00061: Fragmentation dynamics in O$_{2}^{q+}$ and CO$^{q+}$ molecules in intense laser pulses M. Magrakvelidze, C.M. Aikens, U. Thumm We investigate influence of non-adiabatic couplings on the dissociation and Coulomb-explosion (CE) dynamics of diatomic molecules in intense laser fields. To identify electronic states that contribute to the molecular dynamics, we first calculate adiabatic potential curves and electric dipole-coupling (DC) elements with the quantum chemistry code GAMESS.\footnote{M. W. Schmidt et al., J. Comput. Chem. 14, 1347-1363(1993)} Next we calculate fragment-kinetic-energy-release (KER) spectra as a function of time and quantum-beat frequency\footnote{M. Magrakvelidze et al., PRA 79, 033410 (2009)} for one molecular potential curve at a time and compare calculated revival times and beat frequencies with experimental data.\footnote{S. De et al., PRA 82, 013408 (2010)} After identifying relevant electronic states we include laser-induced DCs in improved wave-packet propagation calculations including two (or more) electronic states and again compare KER spectra with experimental results.\footnote{Ibid.} We apply this scheme to O$_{2}$ and CO. [Preview Abstract] |
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L1.00062: Alignment dependence in the breakup of the H$_2$ molecule by xuv laser pulses Xiaoxu Guan, Klaus Bartschat, Barry I. Schneider We present predictions of angular distributions for two-photon double ionization of the hydrogen molecule by a short laser pulse with a central photon energy of 30~eV. Using the fixed-nuclei approximation, the laser-driven electronic wave packets are obtained by solving the time-dependent Schr\"odinger equation in two-center elliptical coordinates with the inter\-nuclear distance fixed at 1.4~bohr. In addition to the parallel and perpendicular geometries, we explore the dependence of the angular distribution on the relative orientation of the molecular axis and the linear polarization vector of the laser field. The individual contributions from the $^1\Sigma_{\rm g}$ and $^1\Delta_{\rm g}$ channels are found to be very sensitive to both the orientation angle and the direction of the reference electron that is observed at a fixed angle with a preset energy. The resulting interference effect between the different ionization channels is analyzed in detail. [Preview Abstract] |
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L1.00063: Time-resolved observation of molecular torsional dynamics C.B. Madsen, J.L. Hansen, L.B. Madsen, H. Stapelfeldt We recently presented the first efforts made to extend the methods of alignment to manipulating and observing the torsion in a molecule [1,2]. Experimental and theoretical results obtained through the joint effort of four Aarhus groups from experimental strong-field laser physics, theoretical physics, theoretical quantum chemistry, and organic synthetic chemistry, demonstrated that strong-field laser physics methods and time-resolved measurements are not limited to small linear molecules, but can actually be useful for studying exciting fundamental phenomena in larger complex systems. Lately, we have explored the torsional dynamics on long time scales (ps). These studies revealed the decay of the torsional oscillation in time. Theoretical efforts are made to explore how energy dissipates from the torsional degree of freedom into overall rotation of the molecule. \\[4pt] [1] C.~B.~Madsen \textit{et al.}, Phys. Rev. Lett. {\bf 102}, 073007 (2009).\newline [2] C.~B.~Madsen \textit{et al.}, J. Chem. Phys. {\bf 130}, 234310 (2009). [Preview Abstract] |
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L1.00064: On dynamical symmetry breaking in the CO$_{2}$ molecule induced by the shaped x-ray pulses Nilam Jadav, Svetlana Malinovskaya Electronic symmetry selection rules are the prime conditions for resonant x-ray scattering of molecules. However in highly symmetrical molecules, these rules may be violated owing to the coupling between electronic states having different spatial symmetry by nuclear motion. We consider the CO$_{2}$ molecule as an example, with the Oxygen x-ray emission spectra manifesting dynamical symmetry breaking in linear molecules. This occurs owing to interactions between close lying core-excited states via asymmetric stretching vibration. The effect of pulse shapes on the population dynamics of the gerade and ungerade core-excited states in the CO$_{2}$ molecule is demonstrated aiming to reveal the pulse parameters that control dynamical symmetry breaking. [Preview Abstract] |
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L1.00065: Selection rules in few photon double ionization Hongcheng Ni, Shaohao Chen, Camilo Ruiz, Andreas Becker We performed numerical simulations using a 3D model for He atom interacting with an intense ultrashort laser pulse. The results of our numerical simulations reveal a selection rule in few photon double ionization, namely in $N$-photon processes (with $N$ odd) the two ionized electrons cannot be emitted back-to-back, while this is allowed when $N$ is even. Furthermore, the difference between momentum space wavefunction projected onto plane waves and projected onto Coulomb wavefunction for the correlation between the two electrons is investigated. [Preview Abstract] |
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L1.00066: Coherent control of nonresonant two-photon excitation in molecules Jing Su, Shaohao Chen, Agnieszka Jaron-Becker, Andreas Becker We extend coherent control schemes of nonresonant two-photon excitation from the atomic case to the molecular case. In particular, we study the two-photon excitation process induced by a set of laser sub-pulses both in a higher dissociating state and a bound state by solving the time-dependent Schr\"odinger equation. Our results show that for two-photon excitation to a higher dissociating state previous control schemes, validated for the atomic case before, do fail due to the coupling electronic and nuclear motion. For bound states we show that by controlling the time delay and the carrier-to-envelope phase difference between two consecutive Gaussian pulses we can either maximize or minimize the two-photon excitation process to a desired bound state. [Preview Abstract] |
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L1.00067: Two-center interferences and nuclear wave packet imaging in dissociating H$_2^+$ molecule Antonio Picon, Alon Bahabad, Henry C. Kapteyn, Margaret M. Murnane, Andreas Becker Double-slit like interferences similar to those observed by Young in his experiment with light appear also in the photoionization of diatomic molecules. The partial electron waves ejected from the two atomic centers of the molecule take the role of the coherent light waves emerging from the two holes in Youngs experiment. We analyze theoretically and numerically a pump-probe scenario with two attosecond pulses in the hydrogen molecular ion. The first attosecond pulse induces the dissociation of the molecule, the second attosecond pulse is ionizing the molecule. By varying the delay between the pump and probe pulses we show how the two-center interferences allow to image main features of the nuclear wave packet, namely its velocity, internuclear distance, and spreading. [Preview Abstract] |
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L1.00068: H$_2^+$ dissociation fragments alignment after few-cycle pulse at mid-infrared regime Shuo Zeng, Fatima Anis, Brett Esry By solving the time-dependent Schr\"odinger equation for H$_2^+$ numerically including nuclear rotation for H$_2^+$, we systematically analyzed the H$_2^+$ rotational dynamics after a few-cycle laser pulse for wavelengths in the range 800-2000~nm. This study extends our test of the axial recoil approximation reported in [1] to longer wavelengths. Individual initial vibrational states show different rotational behavior. Generally, dissociation fragments from lower vibrational states tend to anti-align along the laser polarization direction, while the fragments from higher initial states tend to align along the polarization direction. In addition, we found that the carrier-envelope phase does not influence the post-pulse rotation substantially even for the few-cycle pulse. \\[4pt] [1] F. Anis, T. Cackowski, and B. D. Esry, J. Phys. B 42, 091001 (2009) [Preview Abstract] |
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L1.00069: Creating double core hole two sites in N$_2$ molecules using the Linac Coherent Light Source Li Fang, Brendan Murphy, Timur Osipov, Pavle Juranic, Nora Berrah, Edwin Kukk, Motomichi Tashiro, Masahiro Ehara, Kiyoshi Ueda, Kevin C. Prince, Robert Richter, Raimund Feifel, Peter Salen, Peter van der Meulen, Henning Schmidt, Richard D. Thomas, Mats Larsson We have measured double core hole two sites in N$_2$ molecules using the intense short x-ray laser pulses from the Linac Coherent Light Source free electron laser. This is achieved within the time scale of the single-core-hole state lifetime via sequential core ionization. This work extends previous work [1, 2] and demonstrates that both photoelectron and Auger spectroscopy allow the measurement of double core hole two sites. The latter are very sensitive to the chemical environment and present a new chemical analysis tool. This work was supported in part by the DOE-SC-BES, Chemical Sciences, Geosciences and Biosciences Division. [1] L.~Fang \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 083005 (2010). [2] J.~Cryan \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 083004 (2010). [Preview Abstract] |
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L1.00070: X-ray Split and Delay System for Soft x-ray Pump/Probe Experiments at the LCLS Free Electron Laser Brendan Murphy, John Bozek, Jean-Charles Castagna, Nora Berrah We will report on the development of a mirror based x-ray split and delay system (XRSD) for soft x-rays at the Linac Coherent Light Source free electron laser. This device will be used for x-ray pump, x-ray probe experiments in gas-phase as well as solid state using the LCLS femtosecond photon beam. The XRSD system will be positioned after the Kirkpatrick-Baez focusing mirrors, delivering two pulses with a variable delay to the interaction chamber. Delay of 0-100 femtoseconds can be produced with resolution under 100 attoseconds. The energy in each pulse will be measured shot to shot. The XRSD is expected to be ready for user experiments in early 2012. [Preview Abstract] |
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L1.00071: Laser induced fragmentation dynamics analyzed using Monte Carlo event generators: the single ionization case M. Ciappina, M. Schulz, T. Kirchner Monte Carlo event generators (MCEG) have shown to be a very powerful tool to tackle the fragmentation dynamics of atoms driven by heavy ions and electrons [1,2]. One of the advantages MCEG offer is the possibility to include in a direct way the experimental conditions in the theoretical calculations. We present in this work an extension of MCEG to treat single ionization of H atoms by laser pulses employing the time-dependent distorted wave approach. We show how the experimental resolution affects the structures present in the angle-resolved photoelectron spectrum and in the electron energy distributions. \\[4pt] [1] M. F. Ciappina {\it et al}. Comp. Phys. Comm. {\bf 181}, 813 (2010); M. Schulz {\it et al}. Phys. Rev. A {\bf 81} 052705 (2010)\\[0pt] [2] M. F. Ciappina {\it et al}., Phys. Rev. A {\bf 82}, 062701 (2010) [Preview Abstract] |
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L1.00072: Multiple Ionization and Fragmentation of $SF_{6}$ using the LCLS Femtosecond X-Ray FEL T. Osipov, L. Fang, M. Hoener, B. Murphy, E. Hosler, C. Bostedt, J.D. Bozek, E. Kanter, S.T. Pratt, S.R. Leone, N. Berrah Sulfur hexafluoride molecules were irradiated by the high intensity FEL beam produced by the LINAC Coherent Light Source (LCLS) of the SLAC National Accelerator Laboratory. The molecules were ionized with pulses of 280 fs duration at 800 and 1000 eV photon energy. The experiment was conducted at the High Field Physics end-station of the Atomic, Molecular and Optical physics hutch. We used electron time-of-flight spectrometers for the high resolution measurements of the product photo- and Auger-electrons energy at five exclusive angular directions and several different retardation settings. Separate ion time-of-flight measurements were taken to identify multiple types of recoiling fragments and their charge states for different FEL pulse durations and photon energies. The combined result of these two approaches provides unique information about the chain of multi-step ionization events and molecular fragmentation pathways of the $SF_{6}$ molecule. [Preview Abstract] |
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L1.00073: Two-photon ionization of Helium studied with the multiconfigurational time-dependent Hartree-Fock method David Hochstuhl, Michael Bonitz The multiconfigurational time-dependent Hartree-Fock method (MCTDHF) is applied for simulations of the two-photon ionization of Helium [1]. We present results for the single- and double ionization from the groundstate for photon energies in the non-sequential regime, and compare them to direct solutions of the Schr\"odinger equation using the time-dependent (full) Configuration Interaction method (TDCI). We find that the single-ionization is accurately reproduced by MCTDHF, whereas the double ionization results only capture the main trends of TDCI.\\[4pt] 1] D. Hochstuhl, M. Bonitz, J. Chem. Phys. 134, (2011) [Preview Abstract] |
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L1.00074: Natural orbitals for electrons and nuclei within the diatomic multiconfiguration time-dependent Hartree-Fock (MCTDHF) method Daniel Haxton, Keith Lawler, C. William McCurdy We discuss natural orbitals in the context of the MCTDHF method for ultrafast dynamics of diatomic molecules with nuclear motion. We show that the natural orbitals for electrons and nuclei, as well as the eigenfunctions other reduced density operators which could be called natural wavefunctions, are a useful tool for visualization, similar in some respects to a diabatic basis. Furthermore through the Schmidt decomposition, these objects provide the most compact representation of a wavefunction with interacting degrees of freedom. The natural wavefunction electronic state basis is an alternative to the (dressed) Born-Oppenheimer representation and we show the Schmidt decompositions of various diatomic MCTDHF wavefunctions in short laser pulses. We compare the Schmidt decomposition of H$_2^+$ in prolate spheroidal coordinates (which are parametric) against that in nonparametric coordinates (e.g. cartesian or cylindrical) and discuss the implications for the multielectron problem. These bases may provide an advantageous numerical framework and we outline implementations of various schemes for propagating natural orbitals within our diatomic MCTDHF code. [Preview Abstract] |
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L1.00075: 3D classical ensemble modeling of non-sequential double ionization: the dependence of double-ionization yield on the nucleus Stanley Haan, Katherine Shomsky, Nathan Danks In 3D classical modeling of non-sequential double ionization, we find that plots of double ionization yield vs laser intensity show strong dependence on an adjustable nuclear softening parameter. We explore why, and uncover chaotic behavior and strong sensitivity to interaction with nucleus in recollision excitation with subsequent photoionization. [Preview Abstract] |
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L1.00076: Visualizing the influence of Coulomb force on electron wavepackets in a strong laser field Predrag Ranitovic, S. Witte, D. Hickstein, C. Ding, P. Arpin, M. Vrakking, Y. Huismans, N. Toshima, X.M. Tong, X. Zhou, P. Johnsson, H.C. Kapteyn, M.M. Murnane By combining strong-field ionization with 2D electron momentum imaging, we demonstrate a high degree of control over electron trajectories in the vicinity of the Coulomb potential of the parent ion. The interference between the directly ionized and rescattered electrons strongly depends on the localization of the electron wavefunction in the vicinity of the parent ion at the instant of rescattering. A high degree of control of the electron trajectory is obtained by varying the laser intensity, polarization, phase, and the driving wavelength between 267 nm and 2000 nm. The 2D interference pattern encodes attosecond electron dynamics, as well as information about the size of the returning electron wave packet. Also, the interference between the direct and returning electrons provides a direct measurement of the electron-ion differential cross section, which is found to vary significantly for different atomic and molecular targets. Several different theoretical methods will be presented to support the discussion. [Preview Abstract] |
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L1.00077: Compensation sequences for improved ion addressing in Paul traps True Merrill, Kenneth Brown The use of linear ion chains as quantum registers requires precision control in the intensity, duration, and spatial alignment of laser pulses. Employing compensation pulse sequences can relax these precision requirements by producing accurate gates in the presence of unknown systematic errors. We show that systematic addressing errors caused by beam misalignment and the finite bleed-through coupling of neighboring ions can be corrected to arbitrary accuracy using a family of narrow-band sequences. Furthermore a second class of pass-band sequences can compensate simultaneous systematic errors in addressing and pulse area, however at reduced efficacy. An experiment designed to test these findings is discussed. [Preview Abstract] |
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L1.00078: Dynamics of slow dissociation of D$_{3}^{+}$ in intense ultrashort laser pulses B. Gaire, J. McKenna, M. Zohrabi, K.D. Carnes, I. Ben-Itzhak We have studied laser-induced slow dissociation of D$_{3}^{+}$, which is a benchmark polyatomic system, using an improved coincidence three-dimensional momentum imaging method. In our measurements, we clearly separate and distinguish between all fragmentation channels and measure kinetic energy release down to 0 eV within the experimental resolution. Our results for D$_{3}^{+}$ dissociation suggest that two-body breakup is dominant over three-body fragmentation and that the low kinetic energy release is associated with the D$^{+}$+D$_{2}$ dissociation channel. We explore the pathways for such slow dissociation and further test their validity by changing laser pulse duration and wavelength. Our observations show that slow dissociation is more dominant using ultrashort pulses at 790 nm than at 395 nm, yet the total dissociation rate integrated over all kinetic energies is higher at 395 nm. [Preview Abstract] |
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L1.00079: Supersymmetric phase-equivalent potentials for atoms in intense laser fields J.V. Hern\'andez, B.D. Esry Our work tests the basic assumption of the single-active-electron approximation: that any model which reproduces the bound spectrum --- and ideally also the scattering properties --- should provide a good approximation to the entire multi- electron system. In particular, we use two distinct methods that reproduce the energetic properties of the original effective one-electron potential and still exactly remove the Pauli excluded states. The first is a close- coupling approach, and the second is a grid method that utilizes principles of supersymmetric quantum mechanics~[1] to create a phase- equivalent potential that removes the unwanted states and exactly reproduces the scattering phase shifts at all energies~[2]. Despite retaining all of the properties of the original effective potential, we find quantitative differences in the physical observables given by the two methods and discuss their origin. [1] E.~Witten, Nuc. Phys. B {\bf 188}, 513 (1981). [2] D.~Baye, Journal of Physics A {\bf 20}, 5529 (1987); R.~D.~Amado, Phys.~Rev.~A {\bf 37}, 2277 (1988); D.~Baye and J.~M.~Sparenberg, Phys.~Rev.~Lett. {\bf 73}, 2789 (1994); E.~Garrido, D.~V.~Fedorov, and A.~S.~Jensen, Nuc. Phys. A {\bf 650}, 247 (1999). [Preview Abstract] |
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L1.00080: Effects of Magnetic Field on Classical Ionization Patrick Grugan, Michael Videtto, Christopher Mancuso, Sui Luo, Barry Walker Classical equations of motion are solved numerically for one electron atoms in an intense laser pulse. The study investigates the influence of the laser magnetic field on ionization and rescattering. Many models of electron ionization have ignored the magnetic field of the laser pulse, but recent work has looked at the magnetic field's role in stabilization [1]. Work has been done to show that in the ultra-strong regime (intensities of $\sim $10$^{18}$ W/cm$^{2})$ the laser magnetic field has an influence on rescattering [2]. Specifically, drift of the ionized electron along the laser propagation direction. We use a classical model of the atom, atomic number Z, with one electron and numerically integrate two sets of equations of motion, those with and those without the laser magnetic field. Observable quantities, such as electron radius and energy, are calculated and compared. The data shows that the laser magnetic field does have some influence on ionization, specifically on electron dynamics before ionization and the time required for ionization.\\[4pt] [1] L. N. Gaier and C. H. Keitel, PRA 65, 023406 (2002).\\[0pt] [2] S. Palaniyappan, I. Ghebregziabher, A. Dichiara, J. MacDonald, and B. C. Walker, PRA 74, 033403 (2006). [Preview Abstract] |
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L1.00081: Measurement of laser-induced molecular alignment in cold, low density targets using femtosecond degenerate four wave mixing Xiaoming Ren, Varun Makhija, Vinod Kumarappan A femtosecond degenerate four wave mixing (DFWM) technique for measuring the laser induced non-adiabatic alignment of asymmetric top molecules in a dilute gas jet is reported. The alignment is probed using three beams in a folded BOXCARS geometry. By generating the three beams using a physical mask in a single probe beam, automatic overlap in space and time is obtained. By scanning the pump-probe delay and measuring the background-free DFWM signal, the alignment of rotationally-cold and low-density molecular targets can be rapidly characterized. We demonstrate the technique by measuring the alignment low-density iodobenzene in a high-pressure helium jet. This scheme can also be used with arbitrarily-shaped aligning pulses and pulse sequences, and for a wide variety of molecules. [Preview Abstract] |
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L1.00082: Dynamic modification of the fragmentation of autoionizing excited states of O$_{2}^{+}$ W. Cao, G. Laurent, S. De, M. Schoeffler, T. Jahnke, A. Alnaser, I. Bocharova, C. Stuck, D. Ray, M. Kling, I. Ben-Itzhak, T. Weber, A. Landers, A. Belkacem, R. Doerner, C.L. Cocke The dynamic process of fragmentation of excited states of molecular oxygen is investigated in a two-part study. First, using monochromatic 41 eV radiation and COLTRIMS detection of O+/O+ ion pairs and associated electrons, we establish that this channel is populated only by an indirect process enabled by autoionization of excited oxygen neutrals, and identify the final active molecular states involved. Second, we probe the dynamics of this process using an attosecond pulse train of 35-42 eV EUV, followed by an intense laser pulse (5.10$^{11}$ W/cm$^{2})$. A model gives qualitative agreement with experiment.Supported by Chem. Sci. DOE DE-FG02-86ER1349, NSF CHE-0822646 and USARO W911NF-07-0475 [Preview Abstract] |
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L1.00083: Time Resolved Detection of Native Molecular Emissions and Recombination using Femtosecond Laser Induced Breakdown Spectroscopy from Organic Compounds Jorge Martinez, Charlemagne Akpovo, Nathan Bullock, Susan Allen, Lewis Johnson Laser induced breakdown plasmas are ``dirty'' events yielding a mixture of ionized species, electrons, and non-ionized matter of various size. Molecular emissions have been detected in excited nanosecond plasmas microseconds after the ablation event. However, with these molecular signatures it is difficult to distinguish between native emissions and atmospheric recombination with respect to the sample probed. A time resolved study during and after the continuum of the plasma event produced from specific organic materials can yield a possible insight in identifying native molecular emission and recombination. In this study, a plasma was formed by interacting a femtosecond beam with Nitrobenzoic acid, Ammonium Nitrate, Benzylacetonitrile, Nitrophenol, and Phthalimide. Molecular spectral signatures of NO, OH+, CN, $C_2 $, and NH were monitored as a function of plasma lifetime, with a 50 nanosecond gate window, delineating a trend of growth and decay. Use of a buffer gas, Argon, has been observed suppressing the impact of atmospheric oxygen, nitrogen, and hydrogen on plasma assisted recombination. [Preview Abstract] |
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L1.00084: Potential Barrier Effects in Multiphoton Ionization Processes Liang-Wen Pi, Anthony F. Starace Potential barriers in the effective radial potential experienced by a photoexcited electron are shown to result in dramatic, resonance-like effects in multiphoton ionization processes. In a multiphoton ionization process, such potential barriers may affect not only the final state of the electron (as in single-photon ionization), but also the intermediate- state electron wave packet at energies in the vicinity of the barrier. Such effects have been demonstrated numerically as a function of frequency [1], confirming an experimentally- observed enhancement in two-photon ionization of Xe at a single frequency [2]. We show here that these effects are general by considering the n-photon cross sections (with n$>$2) for ionization of Ar and Xe within a single-active-electron, central-potential model.\\[4pt] [1] L.W. Pi and A.F. Starace, Phys. Rev. A \textbf{82}, 053414 (2010).\\[0pt] [2] V. Richardson \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 013001 (2010). [Preview Abstract] |
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L1.00085: The Nature of Infinity in Quantum Field Calculations Richard Kriske In many textbooks on Quantum Field Theory it has been noted that an infinity is taken a circle and the flux is calculated from the A field in that manner. There are of course many such examples of this sort of calculation using infinity as a circle. This author would like to point out that if the three dimensions of space are curved and the one dimension of time is not, in say a four space, infinity is the horizon, which is not a circle but rather a sphere; as long as space-time is curved uniformly, smoothly and has positive curvature. This author believes the math may be in error, since maps of the CMBR seem to indicate a ``Swiss-Cheese'' type of topology, wherein the Sphere at infinity (the Horizon of the Universe), has holes in it that can readily be seen. This author believes that these irregularities most certainly have a calculable effect on QED, QCD and Quantum Field Theory. [Preview Abstract] |
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L1.00086: Final state distributions of Li Rydberg atoms at high scaled microwave frequency Joshua Gurian, Haruka Maeda, Thomas Gallagher We present experimental results of final state distributions of non-ionized Rydberg atoms in the presence of a microwave field of frequency $\omega$, where the scaled frequency, or ratio of $\omega$ to the classical Kepler frequency, $1/n^3$, is much greater than one. Recent microwave ionization experiments of Rydberg atoms at high scaled frequency have exhibited a strong periodicity in the ionization rate as a function of binding energy, where the period is determined by the energy of the microwave photon. However, the distribution of final states for the remaining bound atoms does not exhibit a similar periodicity, and is markedly different at ten, five, or one photon to the ionization limit. Notably, we observe population trapped in high lying $n$ states one microwave photon below the ionization limit when the initial state is an integer number of microwave photons below the limit, indicating that the coupling of this last bound state to the continuum is what mediates multiphoton microwave ionization. [Preview Abstract] |
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L1.00087: Coulomb explosion imaging of small organic molecules at LCLS Benjamin Erk, Artem Rudenko, Daniel Rolles, Benedikt Rudek, Lutz Foucar, Sascha Epp, Max Cryle, Ilme Schlichting, Christoph Bostedt, Sebastian Schorb, John Bozek, Arnaud Rouzee, Axel Hundertmark, Frank Filsinger, Lauge Christensen, Kiyoshi Ueda, Joachim Ullrich Fragmentation of small organic molecules by intense ultrashort X-ray free-electron laser (FEL) pulses (2000eV, 0.4-2mJ, 3-200fs) has been studied using Coulomb explosion imaging. The experiment was conducted in the CFEL-ASG Multi-Purpose (CAMP) end station installed at the AMO beamline of the Linac Coherent Light Source (LCLS) at Stanford. In order to increase and localize X-ray absorption we used methylselenol, ethylselenol and phenylselenol compounds containing heavy selenium atom as a substitute for naturally occurring oxygen. By measuring kinetic energies and emission angles of few ionic fragments in coincidence, we can separate different fragmentation pathways and reconstruct molecular geometry (bond lengths and angles) at the moment of explosion. The results yield unique information on the structural rearrangement the molecule undergoes upon few-photon absorption, in particular, pointing to the ultrafast charge redistribution within the molecule, which has direct implications for the radiation damage induced by intense X-ray pulses. [Preview Abstract] |
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L1.00088: Theory of Coherent Anti-Stokes Raman Scattering Taking into Account Propagation Effects Alexander Quinn, Svetlana Malinovskaya Inelastic scattering of light in a material causes electrons to jump from one state to another. When three different frequencies of laser light are guided into a material, light emitted from the material is coherent. This ``anti-Stokes'' emission frequency is equal to the frequencies of the ``pump'' and ``probe'' beams minus that of the ``Stokes'' beam. The population of electrons in a given state changes in a relationship proportional to the lasers' applied electric fields. Our research focuses on finding general solutions of semiclassical differential equations for the fields coupled to the Liouville-von Neumann equation that describes dynamics in a molecular system in coherent anti-Stokes Raman scattering. Different approximations are used to determine the rate of change of population in vibrational states. For the case of a large one-photon detuning, the adiabatic elimination, which sets the time derivative of the excited state(s) equal to 0, is applied. We also invoke the rotating-wave approximation, which neglects rapidly-oscillating terms of order exp(-2i*omega*t). [Preview Abstract] |
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L1.00089: Manipulation of Ultracold Rubidium Atoms Using a Single Linearly Chirped Laser Pulse Thomas Collins, Svetlana Malinovskaya The ability to manipulate ultracold atomic and molecular systems allows us to utilize their potential for use in the emerging field of quantum computing, which holds the promise of developing computing systems which operate at speeds far greater than those of conventional computers. Also, ultracold atomic and molecular systems have possible chemical applications that make it desirable to find an efficient way to control which quantum states available to the system are occupied. In this work we studied the behavior of Rubidium atoms dressed by a linearly-chirped laser pulse, modeling the quantum states of the atoms as a three level lambda system. We set as our control knobs the pulse duration, chirp parameter, field strength, and the one-photon detuning. We discovered certain sets of values for the control knobs which yielded near total transfer to the desired state and thus may be used in experimental setup. [Preview Abstract] |
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L1.00090: Tip-based electron source for femtosecond electron diffraction Jan-Paul Stein, Markus Schenk, Johannes Hoffrogge, Michael Kr\"uger, Peter Baum, Peter Hommelhoff In today's femtosecond electron diffraction and microscopy experiments, femtosecond UV pulses are employed to trigger photoemission of electrons from a flat metallic surface cathode. Subsequently, the electrons undergo acceleration in an electric field. By careful choice of the laser intensity profile and compression of the electron bunches via rf-cavities and electron optics sub-100 fs electron pulses have been achieved in the state of the art experiment. The aim of this study is to replace the flat cathode by a sharp metal tip with a radius in the one hundred nanometer regime. Due to the tip geometry the electric field at the apex is greatly enhanced so that electrons experience a strong acceleration right after emission. Electrons leaving the tip with different initial kinetic energies therefore develop a significantly lower timing jitter during their propagation, translating into pulse durations on the order of several tens of femtoseconds at the target, as inferred from simulations. Furthermore, the electron beam emittance decreases drastically. We will present results of a detailed analytic and numerical analysis of different setup parameters and discuss the current experimental status. [Preview Abstract] |
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L1.00091: Photoemission by Large Electron Wave Packets Michael Ware, Justin Peatross, Eric Cunningham The quantum wave packets of free electrons naturally spread, quickly reaching the scale of optical wavelengths. Moreover, electron wave packets born through ionization in an intense laser focus are pulled apart by sharp field gradients. Different parts of the same electron wave packet may even be propelled out opposite sides of the laser focus. The question naturally arises as to how wave packets scatter laser radiation if they undergo such highly non-dipole dynamics. At least two approaches have been used to analyse this problem in the literature, which give differing predictions for radiation strength. We provide an update on an experimental effort to measure the radiation from individual electron wave packets that are spread over an area on the scale of an optical wavelength. [Preview Abstract] |
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L1.00092: Slalom Channeling of Trojan Electrons in 1-Dimensional Ion Chains in Linearly Polarized Electromagnetic Field Matt Kalinski We have recently discovered that two positively charged ions placed in the linearly polarized (LP) field aligned with to the symmetry line joining the ion charges and with the frequency twice the closed motion can support stable nondispersing Trojan wavepackets moving on perfectly 8-shaped trajectories [1]. Here we show that halfs of such trajectories can be connected to spline into long range oscillatory motion in the linear chain of positively charged ions. This results in long distance slalom channeling of electron travelling in Trojan state for a distance of large multiple of the ionic lattice constant. To keep the wavepacket nondispersing the LP field polarization must be perpendicular to the electron motion and strictly adjusted to the the period when the packet is passing and avoiding the neighboring ions. The channeling event is extremely rare in the phase space and requires the precise choice of the wave packet momentum and the initial position at the beginning of the long range oscillatory motion. For the majority of wrong initial conditions the motion results in fast trajectory binding on one of the chain ions. Numerical simulations with the split operator method are also provided. [1] M. Kalinski, ``Trojan-Like Wavepackets on 8-shaped orbits in Linearly Polarized Elctromagnetic Field in Hydrogen Ion Molecule,'' FiO 2009/LS XXV Annual Meeting, San Jose, California, October 2009. [Preview Abstract] |
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L1.00093: ATOMIC AND MOLECULAR PHOTO PROCESSES |
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L1.00094: Role of multiphoton excitation and two-electron effects in high harmonic generation of H$_2$: a TDDFT calculation Xi Chu, Patrick Memoli Using two different TDDFT methods, we study the role of electronically excited states and two-electron dynamics in high harmonic generation (HHG) of H$_2$. The two methods produce slightly different electronic structures as reflected in the calculated ionization potentials. They nevertheless give similar HHG spectra. The difference between the two methods increases with the laser intensity, while their predictions remain qualitatively consistent. Our results suggest that two-electron dynamics can extend the HHG cutoff. Specifics of such an extension depends on the internuclear distance and the laser intensity. We propose an ion excitation plus tunneling ionization mechanism to explain these extensions. The involvement of excited states is further revealed when we analyze each harmonic as a function of the internuclear distance. We see resonant peaks that are due to multiphoton excitation. These peaks exist above the ionization threshold as well. [Preview Abstract] |
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L1.00095: Numerical simulations of H$_2^+$ and H$_3^{2+}$ in intense ultrashort laser pulses Daniel Weflen, Norio Takemoto, Andreas Becker We developed numerical simulation techniques to analyze H$_2^+$ and H$_3^{2+}$ interacting with intense ultrashort laser fields based on the Crank-Nicholson method and the Born-Oppenheimer approximation. We present results for the ionization probabilities and photoelectron spectrum for both molecular ions, and for circularly polarized light as well as linearly polarized light both on and off the molecular axis. [Preview Abstract] |
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L1.00096: Electric-field-induced dissociation of heavy Rydberg ion-pair states Carlos Reinhold, Shuhei Yoshida, Changhao Wang, Barry Dunning A classical trajectory Monte Carlo approach is used to simulate the dissociation of H$^{+..}$F$^{-}$ and K$^{+..}$Cl$^{-}$ heavy-Rydberg ion pairs induced by a ramped electric field. Such field-induced dissociation is used experimentally to detect ion-pair states and analyze their binding energies. The simulations include the effects of the strong short-range repulsive interaction associated with ion-pair scattering. Their predictions are in good agreement with experimental data for Stark wavepackets probed by a ramped field, demonstrating that many of the characteristics of field-induced dissociation can be well described using a purely classical model. The data also show that states with a given value of principal quantum number (i.e., binding energy) can dissociate over a broad range of applied fields, the exact field being governed by the initial orbital angular momentum and orientation of the state. [Preview Abstract] |
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L1.00097: Free-free transitions in the presence of a Debye potential and laser fields at very low incident electron energies Anand Bhatia We study the free-free transition in electron-hydrogenic systems in the ground state and embedded in a Debye potential in the presence of an external laser field at very low incident electron energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen as monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing Volkov wave function for it. The scattering wave function for the incident electron on the target embedded in a Debye potential is solved numerically by taking into account the effect of electron exchange. We calculate the laser-assisted differential cross sections for free-free transition for absorption/emission of a single photon or no photon exchange. The results will be presented at the conference. [Preview Abstract] |
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L1.00098: THE IRON PROJECT \& THE RMAX PROJECT: Highly excited Core resonances in photoionzation of Fe~XVII and impact on plasma opacities, oscillator strengths of Fe~XIV, and nebular abundance of O II Anil Pradhan, Sultana Nahar, Ethan Palay, Werner Eissner The aims of the Iron Project and the Rmax Project are detailed study of radiative and collisional processes of astrophysically abundant atoms and ions, mainly iron and iron-peak elements, over a wide energy range, from infra-red to X-rays. We will illustrate the dominance of high energy photoexciation-of-core (PEC) resonances in photoionization of Fe~XVII due to strong coupling effects on dipole transition arrays $2p^5 \rightarrow 2p^4 \ (3s,3d)$ in the core and examine PEC and non-PEC resonance strengths for their expanded role to incorporate inner-shell excitations for improved opacities. Comparisons show that the currently available cross sections from the Opacity Project are considerably underestimated. For Fe~XIV, we present preliminary results from a large scale computation where 747 fine structure levels with n $\leq$10, $l\leq$9, and 0.5$\leq J \leq$9.5, and 71,407 electric dipole allowed fine structure transitions have been obtained. We will also demonstrate the fine structure effects on the collision strengths and in very low energy photoionzation for in nebular oxygen abundance. [Preview Abstract] |
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L1.00099: Optical field enhancement and strong-field effects at sharp metal tips Sebastian Thomas, Markus Schenk, Michael Kr\"uger, Peter Hommelhoff We are currently studying strong-field effects at a nanometric metal tip by illuminating it with few-cycle femtosecond laser oscillator pulses. In this setup, the electric field at the tip's surface is significantly enhanced. Local optical field enhancement in the vicinity of metal structures occurs due to geometrical effects and dynamical effects like plasmon resonances. Both are described by Maxwell's equations, which we solve numerically to simulate the electromagnetic field for our experimental configuration. In the simulation, we observe a strongly localized field enhancement that vanishes within a few tens of nanometers from the tip's surface. Furthermore, the enhancement is not symmetric with respect to the tip's axis, which underlines the significance of dynamical effects in our setup. Experimentally, we observe above-threshold photoemission and strong field effects\footnote{M. Schenk, M. Kr\"uger, P. Hommelhoff, PRL 105, 257601 (2010)} even at low pulse energies due to field enhancement. Electron spectra might yield insight into plasmon dynamics on the nanometer-(sub-)femtosecond scale. We report on the current status of simulation and experiment. [Preview Abstract] |
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L1.00100: K-Shell Photoabsorption Cross Sections for the Magnesium Isonuclear Sequence Shahin Abdel-Naby, Fatih Hasoglu, Thomas Gorczyca With the improved spectral resolution of launched X-ray telescopes, there is a demand for highly-accurate K-shell photoabsorption cross sections. Such data are needed for modeling astrophysical plasmas, interpreting the observed spectra from distant cosmic emitters, and determining the elemental abundances of the interstellar medium (ISM). Here we present new calculations for photoabsorption of the entire Mg isonuclear sequence using state-of-the-art $R$-matrix methods, including important spectator Auger broadening and inner-shell relaxation effects. Unlike our earlier work on carbon, oxygen, and neon ions, and the present work on multiply-ionized magnesium, the calculations for neutral Mg and singly-ionized Mg$^{+}$ are complicated by additional M-shell occupancy, which leads to a larger $R$-matrix box and difficulties in implementing the quantum defect theoretical spectator Auger decay method for low-lying resonances. [Preview Abstract] |
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L1.00101: Electronic correlations in double ionization of atoms in pump probe experiments Sebastian Bauch, Karsten Balzer, Michael Bonitz The (correlated) dynamics of few-body systems in strong laser fields is in focus of active research since the last two decades. One example is the famous non-sequential double ionization of Helium. With nowadays experimentally available tools it is possible to investigate these processes on the sub-femtosecond timescale. Typically, a short extreme ultraviolet (XUV) pump pulse is combined with a longer infrared (IR) probe pulse. We present theoretical results based on the time-dependent Schr\"odinger equation for such a pump-probe experiment involving two active electrons [1]. A dramatic change of the double ionization yield with variation of the pump-probe delay is reported. We identify the governing role of electron-electron correlations, through a complex interplay of (1) inner-atomic electron shake up and (2) rescattering with subsequent impact ionization. Our results allow for a direct control of the double ionization yield, and the relative strength of double and single ionization. \\[4pt] [1] S. Bauch, K. Balzer and M. Bonitz, Europhys. Lett. 91 53001 (2010) [Preview Abstract] |
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L1.00102: Time-dependent second Born calculations for model atoms and molecules in external fields Karsten Balzer, Sebastian Bauch, Michael Bonitz Nonequilibrium Green function (NEGF) techniques attract more and more attention when correlated quantum many-particle dynamics [1] is under investigation. Thereby, the solution of the Kadanoff-Baym equation imposes strong challenges on the numerics---especially when applied to finite systems. Here, we extend previous work [2] to nonequilibrium and propagate the NEGF in the two-time domain. To render calculations possible, an efficient distributed memory algorithm has been developed enabling parallel and well-scalable computation of the NEGF. Also, the use of the finite element discrete variable representation greatly simplifies summations over parts of Feynman diagrams. By comparing to TDHF and full TDSE results, we demonstrate that the second Born approximation carries valuable information about correlation effects in atoms and molecules exposed to external fields [3]. As examples, we present results for He, H$_2$ and the LiH modeled in one spatial dimension. In addition, we report on spectral and excited state properties.\\[4pt] [1] S. Bauch, K. Balzer, and M. Bonitz, EPL \textbf{91}, 53001 (2010);\\[0pt] [2,3] K. Balzer, S. Bauch, and M. Bonitz, PRA \textbf{81}, 022510 (2010), PRA \textbf{82}, 033427 (2010). [Preview Abstract] |
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L1.00103: Optical transition of the $^{229}$Th nucleus in a solid-state environment Wade Rellergert, Scott Sullivan, David DeMille, Richard Greco, Markus Hehlen, Justin Torgerson, Eric Hudson We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in $^{229}$Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the $^{229}$Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the precision of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision of $ 3 * 10^{ - 17 } < \Delta f/f < 1 * 10^{ - 15 }$ after 1~s of photon collection may be achieved with a systematic-limited accuracy of $\Delta$f/f $\sim$ 2 * 10$^{ - 16 }$. Improvement by a factor of 10$^2$ to 10$^3$ of the constraints on the variability of several important fundamental constants also appears possible. We report on progress towards evaluation of candidate host crystals. [Preview Abstract] |
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L1.00104: Absolute Photoionization Cross Sections for Br$^{2+}$ in the 4$\it{p}\rightarrow$4$\it{d}$ and 3$\it{d}\rightarrow$4$\it{p}$ Energy Regions A. Aguilar, A.M. Juarez, R.C. Bilodeau, D.A. Esteves, D.A. Hardy, E.C. Red Absolute single photoionization cross-section measurements are reported for Br$^{2+}$ in the 31 eV to 46 eV and 64 eV to 72 eV photon energy ranges. The first energy range includes the low-lying $^2P_{3/2,1/2}$ and $^2D_{5/2,3/2}$ metastable state thresholds and extends for 10 eV above the $^4S_{3/2}$ ground state threshold. Strong photoexcitation-autoionization resonances due to 4p$\rightarrow$$\it{n}d$ transitions are seen in the cross-section spectrum and identified based on a quantum-defect analysis of the series. The systematic behavior of the quantum defect parameter of some of the Rydberg series observed in the Br$^{2+}$ spectrum as well as in previously measured Se$^+$ spectrum, are analyzed as a function of the nuclear charge. The 64 eV to 72 eV energy range contains discrete structure that arises from 3$\it{d}\rightarrow$n$\it{p}$ excitations. The $R$-matrix photoionization cross section calculations of Cummings and O'Sullivan, PRA, 54 (1996) are compared to our absolute cross section measurements in this energy range. [Preview Abstract] |
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L1.00105: Spatial dependence of polarization in optically-pumped Rb vapor cells Joan Dreiling, Eric Norrgard, Dale Tupa, Timothy Gay In optical-pumping of alkali-metal vapors, the polarization of the atoms is typically determined by probing along the entire length of the pumping beam, resulting in an averaged value of longitudinal polarization. Unfortunately, these measurements do not give any information about spatial variations of the polarization along the pump beam's propagation distance. Using a probe beam oriented perpendicular to the pumping beam, we have demonstrated a heuristic method for determining the polarization in a column transverse to the pump beam's axis, allowing us to map the polarization in a rectangular Rb vapor cell. The limits of the accuracy of this method are discussed, and a comparison is made with previously demonstrated techniques for polarization mapping [1].\\[4pt] [1] A.R. Young et al. Appl. Phys. Lett. 70 3081 (1997). [Preview Abstract] |
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L1.00106: Vibrationally-resolved structure in O$_{2}^{+}$ dissociation by intense ultrashort laser pulses M. Zohrabi, J. McKenna, B. Gaire, Nora G. Johnson, K.D. Carnes, I. Ben-Itzhak Laser induced dissociation of O$_{2}^{+}$ is studied in the strong-field limit using a crossed laser--ion beam coincidence 3D momentum imaging method (790 and 395 nm, 40 fs, $\sim $10$^{15}$ W/cm$^{2})$. The measured kinetic energy release spectra from dissociation of O$_{2}^{+}$ reveal vibrational structure never observed before in multielectron molecules, which persists over a wide range of laser intensities. By evaluation of the potential energy curves, we assign the spectral energy peaks to dissociation via a one photon pathway $\vert ^{ }$a$^{ 4 }\Pi _{u }> \quad \to \quad \vert ^{ }$f$_{ }^{4 }\Pi _{g }-_{ }$1$\omega _{ }>$ --- a bond softening mechanism similar to the one observed in H$_{2}^{+}$. Careful inspection unveils an apparent suppression in the dissociation of particular vibrational peaks which is a manifestation of the well-known Cooper minima effect. [Preview Abstract] |
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L1.00107: Comparative Analysis of Double Auger Decay and Two-Step Shake-Off Resulting from the Relaxation of Core Excited Neon M.P. Jones, M. Schoffler, T. Jahnke, K. Kreidi, J. Titze, R. Dorner, C. Stuck, A. Belkacem, Th. Weber, A.L. Landers We have conducted a COLTRIMS experiment at the ALS-LBNL to investigate the core excitation of neon: \textit{Ne + $\gamma \quad \to $ Ne(1s2s}$^{2}2p^{6}3p)$. The subsequent electronic relaxation produced among others, the Ne$^{2+}$ charge state. An analysis of this channel revealed mechanisms that include Double Auger (DA) decay as well as a two-step shake-off process involving the $3p$ electron. In addition, we have studied the energy sharing and angular correlation that takes place between the continuum electrons. These detailed measurements further our understanding of the sequential nature of PCI and the characterization of the DA process. Lastly, we will demonstrate how the series of line energies associated with the shake process can be exploited to produce an extremely sensitive method for calibrating a COLTRIMS spectrometer. [Preview Abstract] |
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L1.00108: Hybrid Devices for Cavity QED in Solid State Systems Brendan Shields, Nathalie de Leon, Luozhou Li, Xuetao Gan, Dirk Englund, Hongkun Park, Mikhail Lukin Solid state emitters such as quantum dots or nitrogen vacancy (NV) centers in diamond are promising systems for implementing scalable quantum information technologies due to their stability and compactness. A key ingredient for scalability is the strong coupling of a narrow-band optical transition to a single photonic mode. This coupling can be achieved by placing the emitters in the mode of a small volume, high-Q optical cavity. Here we present an approach to deterministically place a Gallium Phosphide photonic crystal cavity at the location of an NV center near the surface of a diamond substrate and discuss its experimental implementation. [Preview Abstract] |
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L1.00109: Laser-induced dissociative and nondissociative ionization of molecular ion beams U. Ablikim, B. Gaire, M. Zohrabi, K.D. Carnes, I. Ben-Itzhak We have studied the laser-induced ionization of molecular ion beams such as NO$^{+}$, O$_{2}^{+}$, and CO$^{+}$. We will present a coincidence three-dimensional momentum imaging method that we recently developed [1], which allows the simultaneous measurement of dissociative and nondissociative ionization of molecular ion beams. We measured the nondissociative (e.g. NO$^{++})$ and dissociative (e.g. N$^{+}$+O$^{+})$ ionization yields as a function of laser intensity and pulse duration. Our experimental results suggest that these yields increase with laser intensity toward saturation. We also find that enhanced ionization is the dominant contribution to dissociative ionization; therefore, the channel is suppressed for very short pulses. \\[4pt] [1] B. Gaire, Ph. D Thesis, Kansas State University (2011) [Preview Abstract] |
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L1.00110: Observation and modelling of uneven mode-spacing and frequency-pulling in helium-neon lasers Jeffrey Philippson, Matthew Romerein, Stephen McMurtry, Ralph Shiell The precise optical frequencies emitted by a laser are influenced by both the cavity and the detailed properties of the gain medium. Variation in refractive index in the region around a lasing transition leads to the phenomenon of frequency-pulling due to the presence of the laser cavity. We have explored the dependence of this phenomenon on cavity length for two internal-mirror He-Ne lasers as the bare cavity modes are tuned across the gain profile. The beat between two adjacent modes is seen to fall within two distinct frequency regions, depending on their relative polarizations. We have modelled the effects of specific refractive index profiles and mirror birefringence, and compared them with experimental results. A complete understanding of this effect may provide useful information about laser properties such as the complete gain profile, round-trip losses and nonlinear behavior. [Preview Abstract] |
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L1.00111: Time resolved Compton scattering for a model fermion-boson system R. Wagner, Q. Su, R. Grobe We study the scattering of a boson with a fermion with full spatial and temporal resolution based on the one-dimensional Yukawa Hamiltonian. In quantum field theory this interaction is described by the annihilation and creation of bosons with intermediate virtual particle states. We show that this process can be modeled in the center of mass frame by a scattering potential, permitting us to interpret the absorption and re-emission processes in quantum mechanical terms of a characteristic force. This Compton force between the fermion and boson is repulsive for large distances and attractive for shorter spacings. We also examine the periodic dynamics of a fermion and a boson that are spatially confined to a ring-cavity in which they counter-propagate, enabling us to study interactions independent of the transients that characterize the (one-time) scattering event of two wavepackets. [Preview Abstract] |
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L1.00112: Multiphoton population transfer between rovibrational states of HF Turker Topcu, Francis Robicheaux Efficient population transfer by adiabatically chirping through a multiphoton resonance in microwave driven and impulsively kicked Rydberg atoms has been reported both experimentally and theoretically. Previous work has demonstrated that the physical mechanism responsible for the transition can be viewed as a classical process in phase space as well as a quantum mechanical resonant transition. Here we report on our classical and quantum mechanical simulations in which we have exploited this mechanism to vibrationally excite an HF molecule up to $|\nu=4,J\rangle$ from its ground state using an intense IR pulse. We compare one-dimensional quantum and classical models where there are no rotational degrees of freedom. We find that for low laser intensities, the transition is classically forbidden although it occurs quantum mechanically through tunneling. We show that for larger peak intensities, the transfer can be looked upon as a classical transition in phase space, similar to that observed in the atomic case. We extend our simulations to fully three-dimensional quantum calculations and investigate the effect of coupling between different rotational pathways. We briefly discuss the effect of thermal averaging over the final $J$-states. [Preview Abstract] |
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L1.00113: Electromagnetic Energy Momentum Tensor in a Dielectric Michael Crenshaw, Thomas Bahder The Abraham-Minkowski controversy refers to the century-old inability to decide the energy-momentum tensor for an electromagnetic field traversing a dielectric medium. However, neither the Abraham momentum nor the Minkowski momentum is conserved and we show that the Abraham and Minkowski energy-momentum tensors are constructed from continuity equations, rather than conservation laws, and do not transform as tensors. We show that the Gordon [1] momentum is the unique total momentum in a thermodynamically closed system consisting of the field and a negligibly reflecting dielectric. We construct conservation laws based on the conserved Gordon momentum and use them to construct a symmetric traceless energy-momentum tensor in a coordinate system with time-like coordinate ct/n. \\[4pt] [1] J. P. Gordon, Phys. Rev. A 8 14 (1973). [Preview Abstract] |
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L1.00114: Scattering of Light by Electron Wave Packets: Size Doesn't Matter John Corson, Scott Glasgow, Sebastian Acosta, Michael Ware, Justin Peatross In support of a current experiment, we investigate light scattering by individual free electrons in an intense laser focus using full second quantization. This addresses the question of whether emission from a large electron packet will be suppressed owing to interference between different parts of the packet. Textbook treatments of Compton scattering generally use exact momentum states, but packets necessarily superpose many momentum states with the possibility of quantum interference (see J. Peatross, C. Muller, K. Hatsagortsyan, and C. H. Keitel, Phys. Rev. Lett. \textbf{100}, 153601, 2008). We investigate the details of this interference for both single- photon and coherent-state scattering. Kinematic constraints eliminate interference in the case of unidirectional stimulation, whether the scattering is single- or multi-photon in nature. To all orders of perturbation theory, the scattering exhibits no dependence on the relative phases of constituent momenta, and thus no dependence on wave packet size. [Preview Abstract] |
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L1.00115: Single and double multiphoton ionization of Li and Be atoms by strong laser fields Dmitry Telnov, John Heslar, Shih-I Chu The time-dependent density functional theory with self-interaction correction and proper asymptotic long-range potential is extended for nonperturbative treatment of multiphoton single and double ionization of Li and Be atoms by strong 800 nm laser fields. We make use of the time-dependent Krieger-Li-Iafrate (TDKLI) exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. However, we have found that the discontinuity of the TDKLI potential is not sufficient to reproduce the characteristic feature of double ionization. This may happen because the discontinuity of the TDKLI potential is related to the spin particle numbers only and not to the total particle number. Introducing a discontinuity with respect to the total particle number to the exchange-correlation potential, we were able to obtain the knee structure in the intensity dependence of the double ionization probability of Be. [Preview Abstract] |
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L1.00116: Effect of Coulomb attraction on low-energy structure of ATI spectra Dmitry Telnov, Shih-I Chu Recent experimental observations of above-threshold ionization (ATI) of rare gas atoms and diatomic molecules by mid-infrared laser fields revealed a prominent maximum in the electron energy spectrum very close to the ionization threshold. This low-energy structure (LES) cannot be reproduced by the widely used Keldysh- Faisal-Reiss theories. We have performed a theoretical analysis and fully \textit{ab initio} precision calculations for the hydrogen atom. Our results show that LES is related to the effect of Coulomb attraction in the final state of the electron. The probability density of slow electrons is condensed in the vicinity of the nucleus favoring the ionization process. As a result, the ATI electron energy spectrum increases when approaching the threshold. Our numerical data on the hydrogen atom show a maximum in the energy distribution close to the threshold, similar to the low-energy structure revealed by the experiments. [Preview Abstract] |
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L1.00117: Photoionization of Xe$^{+ }$ion confined in C$_{60}$ fullerene Zhifan Chen, Alfred Z. Msezane Photoionization cross section for the Xe$^{+ }$@C$_{60 }$ endohedral fullerene has been studied using our open-shell random phase approximation with exchange method and a C$_{60}$ model potential. The C$_{60}$ fullerene was described by an attractive short range spherical well with potential V(r), given by V(r) =- V$_{0}$ for r$_{i}<$ r$<$ r$_{0}$, otherwise V(r) =0, V$_{0}$=0.3028 a.u. The wave functions of the Xe$^{+}$ confined inside the C$_{60}$ have been evaluated by solving the Schr\"{o}dinger equation with both regular and irregular solutions and the continuous boundary conditions of the wave functions and their logarithmic derivatives at r$_{i}$ and r$_{0. }$Our calculation included all the intershell coupling among the 4d-$\varepsilon $f, 5s-$\varepsilon $p, and 5p-$\varepsilon $s,$\varepsilon $d transitions. $_{ }$The RPAE equation was solved to obtain the partial cross sections with a total of 12 $^{2}$D states, 9 $^{2}$P states and 6 $^{2}$S states. The photoionization of Xe$^{+}$@C$_{60}$ shows stronger correlated confinement resonances. [Preview Abstract] |
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L1.00118: Photodetachment Cross Sections of Ce$^-$ Lin Pan, Donald R. Beck The photodetachment cross section of Ce$^-$ on the energy range 0.57-0.75 eV has been calculated using the relativistic version of Configuration Interaction in the Continuum formalism by Fano [1] and Mies [2]. Our results are able to interpret all the features in the tunable infrared photodetachment spectroscopy on the same energy range [3,4]. These include two bound to bound transitions and eight transitions to low-lying resonance states. By matching the calculated plot for cross section to the neutral production signal from the experiment, the electron affinity of Ce$^-$ is further defined to be around 0.628 eV, which agrees with the measurement [3]. The binding energy of the first excited state of Ce$^-$ 4f5d$^2$6s$^2$ can also be reliably extracted. The details of the calculation and the identity of each feature will be presented in our poster at the conference.\\[4pt] [1] U. Fano, {\em Phys. Rev.} {\bf 124}, 1866 (1961).\\[0pt] [2] F. H. Mies, {\em Phys. Rev.} {\bf 175}, 164 (1968).\\[0pt] [3] C. W. Walter {\it et al}, {\em Phys. Rev. A} {\bf 76}, 052702 (2007).\\[0pt] [4] C. W. Walter, private communication. [Preview Abstract] |
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L1.00119: Effects of core correlations on the photodetachment of Cu$^{-}$ J. Jose, G.B. Pradhan, G. Aravind, P.C. Deshmukh, V. Radojevic', S.T. Manson The photodetachment of anions is an excellent probe for many-electron correlation effects since the valence electron is only weakly attached to the atom. In the present study the RRPA [1] and MCTD method [2] are employed to investigate the core correlation effects on the photodetachment of Cu$^{-}$ (Z=29) in the low energy region. We included the core correlations by including double excitations from the core 3d subshells besides valence electron excitations. The GRASP92 [3] package was used to obtain the MCDF wave functions. Good agreement of MCTD results with experimental data [4] in the low energy region underlines the significance of core correlation effects. Using the RRPA, we have found a slight deviation of photoelectron angular distribution asymmetry parameter b$_{4s}$ from 2 [5] at the Cooper minimum, within the experimental errors. \\[4pt] [1]. W. R. Johnson and C. D. Lin, Phys. Rev. A \textbf{20}, 964 (1979). \\[0pt] [2]. V. Radojevic' and W. R. Johnson, Phys. Rev. A \textbf{31}, 2991 (1985). \\[0pt] [3]. F. A. Parpia \textit{et al.}, Comput. Phys. Commun. \textbf{94,} 249 (1996) \\[0pt] [4]. P. Balling \textit{et al.}, J. Phys. B \textbf{25}, L565 (1992). \\[0pt] [5]. G. Aravind \textit{et al.}, Phys. Rev. A. \textbf{79}, 043411 (2009). [Preview Abstract] |
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L1.00120: Dramatic quadrupole effects in the low-energy photoionization of the 3s subshell of atomic Mg G. Pradhan, J. Jose, P.C. Deshmukh, S.T. Manson, L.A. LaJohn, R.H. Pratt Calculations have been performed, at the relativistic-random-phase approximation (RRPA) level, of the dipole and quadrupole photoionization of Mg 3s in the threshold region, including interchannel coupling among channels arising from 1s, 2s, 2p and 3s ionization. In the vicinity of the Cooper minima in the 3s$\to \varepsilon $p$_{1/2,3/2}$ dipole channels, in the region of 10 eV photon energy, the results show that the quadrupole cross section is larger than the dipole cross section, the first known instance of such a phenomenon in a realistic calculation; one that includes both the relativistic splitting of the Cooper minima, along with interchannel coupling effects. As a result, the nondipole photoelectron angular distribution parameters are huge in this region and very energy-dependent. This leads to an angular distribution which is highly nondipole and changes dramatically with small changes in energy. This phenomenology, or something similar, should be exhibited in the threshold regions of the photoionization of ns states of low-Z atoms which manifest Cooper minima in the dipole channel. The predicted cross sections, although small, should be large enough for experimental scrutiny of the photoelectron angular distribution. [Preview Abstract] |
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L1.00121: Location of low-energy zeroes in bound-free quadrupole matrix elements and their systematics in comparison to quantum defects and phase shifts L.A. Lajohn, R.H. Pratt, G. Pradhan, T. Banerjee, H. Varma, P.C. Deshmukh, S.T. Manson Using the example of photoionization of 3s and 4s atomic subshells, we study the energies of quadrupole Cooper minima (QCM) over the entire range of Z for which they appear in the continuum. The results show that s$\to $d continuum QCM show up over a much larger range of Z than their s$\to $p dipole (DCM) counterparts. For 3s photoionization QCM exist for Z=11-30, a much larger range than dipole case of Z=11-14; for 4s photoionization, QCM exist for Z=19-50, compared to the dipole case of Z=19-36. Also, for any Z for which both dipole and quadrupole minima exist for a given subshell, the energy location of the QCM is always larger than the energy of the DCM. This phenomenology is related to the phase shifts of the continuum wave and the fact that the d-wave phase shift is always smaller than the corresponding p-wave in the atomic potential, which means that the p-wave is always pulled in towards the nucleus more than the corresponding d-wave. The calculations were performed using fully relativistic Dirac-Slater wave functions over the broad range. In selected cases relativistic-random-phase approximation (RRPA) calculations were also performed. [Preview Abstract] |
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L1.00122: Extension of Multiconfiguration Hartree-Fock method to allow Double Photoionization of Atoms Hari P. Saha Very recently we were successful in extending the multiconfiguration Hartree-Fock (MCHF) method for electron impact ionization of atoms [1,2] to allow double photoionization of atoms. In the meeting we will report, as a test case, the results of double photoionization of helium atom using the extended MCHF method. We will present results of our calculation for triple differential, single differential and total cross section for double photoionization of helium. We have calculated the initial state in the Hartree-Fock (HF) and the MCHF approximations and the final state in the Coulomb and the HF approximation to reproduce the previously published works. We will compare the present results with available theoretical and experimental data. Finally we will discuss our plan how to obtain electron correlation between two final state continuum electrons completely ab-initio. \\[4pt] [1] Hari P. Saha, Phys. Rev. A 77, 062705 (2008)\\[0pt] [2] Hari P. Saha Phys. Rev. A 82, 042703 (2010). [Preview Abstract] |
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L1.00123: Photoionization microscopy of He atoms Aneta Smolkowska, Thomas Bergeman, Arjan Gijsbertsen, Julia Jungmann, Marc Vrakking Since the dawn of quantum mechanics physicists have dreamt of directly observing one of the most elusive quantum objects -- the wave function. The typical length scale that a wave function occupies is the atomic unit of length (a$_{0}$=0.528*10$^{-10}$ m). Although it is quite common to observe objects with similar sizes using various types of near-field microscopy, wave functions are challenging as they change their appearance upon observation. Photoionization microscopy has been found to be an appropriate tool for investigating those quantum objects. A possible experimental set-up comprises two plates that are generating a homogeneous electric field and the photoionization process occurs in the focus of the laser. The two-dimensional flux of launched electrons is pictured on a position-sensitive detector. Characteristic oscillatory patterns in the image result from interference of various classical trajectories by which electrons move towards the detector. Two different concentric structures can be discerned as a direct and indirect ionization process. The number of dark fringes in the image is equal to the number of nodes of the electronic wave function. Here we present an experiment that allows for a direct observation of the nodal structure of the electronic wave function in atomic He. [Preview Abstract] |
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L1.00124: Rescattering theory of electron and ion momentum spectra of non-sequential double ionization of atoms Zhangjin Chen, C.D. Lin We study the non-sequential double ionization of atoms in short strong laser pulses on the basis of recently developed quantitative rescattering (QRS) model. The target dependence, CEP (carrier envelope phase) dependence and intensity dependence of the 2-dimensional correlated momentum spectra for the two outgoing electrons as well as the momentum distributions for the doubly-charged ion are investigated systematically in terms of the contributions from various electron-ion scattering mechanisms. Some of the simulated results are compared with the experimental measurements. [Preview Abstract] |
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L1.00125: Photoionization Cross-Section Measurements in a Rubidium Magneto-Optical Trap Alina Gearba, Brad Crochet, Kileigh Peturis, Charles Young Photoionization cross-section measurements are relevant for fundamental tests of the atomic theory, as well as state-selective detection of trapped atomic and molecular species and plasma research, including ultracold plasma formation. We have extended the current photoionization cross-section measurements of the 5P$_{3/2}$ exited state of rubidium by including three additional wavelengths close to the ionization threshold of 479.1 nm. The measurements were performed in a rubidium magneto-optical trap using several lines from a mixed argon-krypton ion laser ranging from 457.9 nm to 476.5 nm. The photoionization rate for each wavelength was determined from the loss rate of atoms in the trap during exposure to the ionizing laser radiation. Our results are in good agreement with other experimental results and allow for comparison with theoretical predictions of the photoionization cross section versus the ionizing photon energy. [Preview Abstract] |
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L1.00126: Electron wave-packet interference in atomic photoionization by a single few-cycle IR laser pulse Aihua Liu, Uwe Thumm We analyze recently measured [1] interference patterns in the momentum-resolved single-ionization photoelectron spectra from helium by comparing the interference of contributions to calculated photoelectron spectra that originate from a few selected sub-IR-cycle time intervals during the laser-atom interaction. For contributions from just two time intervals that are centered at successive maxima of the laser-electric field with lengths of a few attoseconds, our calculation reproduce the measured interference structure in the momentum-resolved spectra. \\[4pt] [1] R. Gopal \textit{et al.}, Phy. Rev. Lett. {\bf 103}, 053001 (2009). [Preview Abstract] |
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L1.00127: Study of the nonlinear interactions of atomic autoionizing states with ultrashort intense EUV pulses W.-C. Chu, Toru Morishita, C.D. Lin We study theoretically the formation and decay of atomic autoionizing states by intense ultrashort EUV pulses. In the case of the $2s2p(^1P^o)$ resonance in helium, we examined how the electron yields and the shape of the electron spectra (the Fano $q$-parameter) change with the pulse intensity and pulse duration. Results obtained using a theory generalized to short pulses from the earlier models for long pulses [1,2] are compared to \textit{ab initio} calculations based on the numerical solution of the time-dependent Schr\"{o}dinger Equation for the two-electron helium. In view of the emerging intense light pulses from free-electron lasers, the theory will be used to evaluate the condition for observing nonlinear near-resonance photoabsorption for EUV and X-rays.\\[4pt] [1] P. Lambropoulos and P. Zoller, Phys. Rev. A 24, 379 (1981).\\[0pt] [2] L. B. Madsen and P. Lambropoulos, J. Phys. B: At. Mol. Opt. Phys. 34, 1855 (2001). [Preview Abstract] |
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L1.00128: Direct Experimental Observations of a Phase Space Turnstile in a Rydberg System Kevin Mitchell, Korana Burke, Shuzen Ye, Brendan Wyker, Barry Dunning Rydberg atoms exposed to alternating positive and negative electric field pulses (kicks) are an example of a chaotic atomic system. Chaotic ionization in this system is organized by a phase space turnstile which represents a mechanism that promotes electrons from their bound to unbound state. Only the electrons that are inside the turnstile ionize after one kicking period. We present theoretical and experimental results for the turnstile signature in the chaotic ionization of Rydberg atoms. We create a Rydberg wave packet and subject it to alternating kicks, after which we measure the ionization fraction. The signature of the turnstile manifests itself in the step-function-like behavior of the ionization fraction as a function of the kick strength. We show that this behavior persists for different values of kicking periods and starting electron energies. [Preview Abstract] |
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L1.00129: Observations of Bound and Resonance States of Ce$^{- }$ C.W. Walter, Y.-G. Li, D.J. Matyas, R.M. Alton, S.E. Lou, R.L. Field III, N.D. Gibson, D. Hanstorp The negative ion of cerium has been investigated with tunable infrared laser photodetachment spectroscopy. The relative cross section for neutral atom production was measured with a crossed laser-ion beam apparatus over selected photon energy ranges between 0.56 -- 0.7 eV. The spectrum reveals several sharp peaks due to negative ion resonances and possible bound-bound transitions in Ce$^{-}$. The newly observed transitions, together with our previous measurements [1], provide insight into the rich near-threshold spectrum of this lanthanide negative ion.\\[4pt] [1] C.W. Walter, N.D. Gibson, C. M. Janczak, K.A. Starr, A.P. Snedden, R.L. Field III, and P. Andersson, \textit{Physical Review A }\textbf{76}, 052702 (2007). [Preview Abstract] |
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L1.00130: K-shell photodetachment from O$^{-}$ N.D. Gibson, C.W. Walter, D.J. Matyas, Y.-G. Li, R.M. Alton, S.E. Lou, R.C. Bilodeau, N. Berrah, A. Aguilar, D. Hanstorp The K-shell photodetachment spectrum of O$^{-}$ has been investigated using the merged ion-photon beam photodetachment technique. O$^{-}$ ions were produced in a Cs sputtered negative ion source (SNICS II) on a new Movable Ion Photon Beamline (MIPB) while the photons were produced by the undulator on the Advanced Light Source Beamline 8.0.1. Positive oxygen ions formed by multiple detachment were detected as a function of photon energy. Photoexcitation of a $1s$ electron leads to a short-lived Feshbach resonance ~3 eV below the 1s detachment threshold due to the extra stability of the now full $2p^{6}$ shell [1]. The Feshbach resonance is observed near 525 eV in the O$^{+}$, O$^{2+}$ and O$^{3+}$ channels. Comparisons to inner-shell photoionization of O will be discussed for both experiment [2] and theory [3]. [1] Bilodeau RC, \itshape{et al.}\normalfont, Phys. Rev. A, \bfseries72\normalfont, 050701(R), 2005. [2] Stolte WC, \itshape{et al.}\normalfont, J. Phys. B, \bfseries30\normalfont, 4489, 1997. [3] Gorczyca TW, McLaughlin BM, J. Phys. B, \bfseries33\normalfont, L859, 2000. *This material is based in part upon work supported by the National Science Foundation under Grant No. 0757976 and by DOE, Office of Science, BES, Chemical Sciences, Geosciences and Biosciences Divisions. The ALS is supported by DOE, Office of Science, BES. DH acknowledges support from the Swedish Research Council. [Preview Abstract] |
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L1.00131: K-shell x-ray spectroscopy of atomic nitrogen Dennis W. Lindle, Marcelo Sant'Anna, Alfred S. Schlachter, Gunnar Ohrwall, Wayne C. Stolte, Brendan M. McLaughlin Absolute K-shell photoabsorption cross sections for atomic nitrogen have been obtained experimentally and theoretically. Previous high-resolution K-shell measurements for this important atom have never been reported because of the difficulty of making a sufficiently dense target of nitrogen atoms. Interplay between experiment and theory enabled identification and characterization of strong np resonance features appearing throughout the 1s threshold region. An experimental value of 409.64 +/- 0.02 eV was determined for the K-shell binding energy of N. [Preview Abstract] |
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L1.00132: K-shell photoionization of Be-like B$^+$ ions A. M\"{u}ller, S. Schippers, R.A. Phaneuf, S.W.J. Scully, A. Aguilar, A.S. Schlachter, M. Gharaibeh, C. Cisneros, B.M. McLaughlin Absolute cross sections for K-shell photoionization of Be-like B$^+$ ions were measured employing the photon-ion merged-beam technique at the Advanced Light Source in Berkeley. By using high-resolution spectroscopy with E/$\Delta$E up to 8800 the energy ranges 193.7~eV to 194.7~eV and 209.5~eV to 215~eV were covered. Lifetimes of the strongest resonances were determined with a relative uncertainty as low as about 4\% for the broadest resonance. Moreover, resonance energies could be measured with absolute uncertainties of less than 30 meV. The experimental resonance parameters, i.e., strengths, energies and natural widths, compare favorably with theoretical results obtained with the R-matrix method. Agreement is also found with heavy-ion storage ring experiments where the 1s2s2p$^2$ $^3$D resonance was observed in B$^{2+}$ ion-electron photorecombination which is time-reversed photoionization of B$^+$. The present photoionization data were obtained for a mixture of B$^+$ ions in the 1s$^2$2s$^2$ ground state and the 1s$^2$2s2p $^3$P$^o$ metastable states, respectively. The measured resonance strengths are consistent with 60\% ground- state and 40\% metastable-state ions in the primary ion beam. [Preview Abstract] |
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L1.00133: Double photoionization of atomic ions in high frequency radiation fields M.S. Pindzola, F. Robicheaux, J. Colgan In support of planned experiments involving the photoionization of atomic ions at LCLS/SLAC and FLASH/DESY using EBITs, we have derived time-dependent close-coupling equations for both the Schrodinger and Dirac equations which track the correlated three body breakup of a two-electron atomic ion in the presence of an attosecond high frequency radiation field. For the double photoionization of Ne+8 and U+90, we calculate the strengths of electric dipole and quadrupole radiation field effects on the energy and angular correlated motion of the two photoelectrons. [Preview Abstract] |
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L1.00134: Photoionization of spherical fullerenes: Dependence of the strength and lifetime of plasmon resonances on the number of carbon atoms Matt McCune, Ruma De, Himadri Chakraborty, Mohamed Madjet, Steve Manson The time-dependent local density approximation is used to calculate the total and subshell-differential photoionization cross sections of a number of spherical carbon fullerenes C$_{N}$. For each system the core comprised of $N$ number of C$^{4+}$ ions is smeared into a classical jellium hull before treating the correlated motion of 4$N$ valence electrons quantum mechanically in the Kohn-Sham formalism [1]. Results show two collective plasmon resonances in each fullerene system as expected from previous studies on C$_{60}$ [2]. The peak values and the lifetimes of these resonances, however, exhibit diverse variations as a function of $N$. In general, while the maximum value of the low-energy plasmon (LEP) increases as the second power of $N$, deviations from such simple scaling are found for the high-energy plasmon (HEP). On the other hand, the lifetime of the LEP suggests a near linear increase with $N$ but for the HEP the variation of the lifetime with $N$ shows non-monotonic behavior.\\[4pt] [1] Madjet et al., \textit{J. Phys.} B \textbf{41}, 105101 (2008);\\[0pt] [2] Scully et al., \textit{Phys. Rev.Lett.} \textbf{94}, 065503 (2005). [Preview Abstract] |
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L1.00135: Photoionization of bilayer fullerene onions Ruma De, Matt McCune, Himadri Chakraborty, Mohamed Madjet, Steve Manson Density functional approaches are employed to calculate the photoionization cross sections of the C$_{60}$@C$_{240}$ system -- a prototype bi-layer fullerene onion. The core of C$^{4+}$ ions is smeared into a jellium-type double-shell structure before treating the correlated motion of all valence electrons in the standard Kohn-Sham framework [1]. In the low photon-energy regime dominated by the electronic collective motion, plasmon resonances appear whose character exhibits significant influence of the dynamical bilayer coupling. In the high energy region, on the other hand, the quantum interference effects induce oscillations far richer in frequency-structures than previously observed for monolayer fullerenes [2, 3]. The results indicate that hybridizations between near-degenerate pure orbitals of the constituent monolayers produce significant imprints on the overall ionization phenomenology.\\[4pt] [1] Madjet et al., \textit{J. Phys.} B \textbf{41}, 105101 (2008);\\[0pt] [2] Ruedel et al., \textit{Phys. Rev. Lett.} \textbf{89}, 125503 (2002);\\[0pt] [3] McCune et al.,\textit{ J. Phys.} B \textbf{41}, 201003 (2008). [Preview Abstract] |
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L1.00136: Double Photoionization of Pyrrole, Furan, and Thiophene Emily Makoutz, Tim Hartman, Narayana Appathurai, Ralf Wehlitz We have studied the double-to-single photoionization ratio for the aromatic molecules pyrrole, furan, and thiophene over photon energies ranging from 20 to 180 eV. Our goal is to compare the behavior of the ratios of these molecules as a function of photon energy. The three molecules have the same basic structure (a five-member-ring) that differs by a single atom. The overall goal is to find a systematic behavior of the double-to-single photoionization ratio for various organic molecules. By studying different hydrocarbons that vary in structure and/or atomic members, we were able to identify three basic double photoionization mechanisms that can contribute to double photoionization. However, not all hydrocarbons exhibit all three mechanisms. [Preview Abstract] |
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L1.00137: Visualizing electron rearrangement in space and time during the transition from a molecule to atoms Agnieszka Jaron-Becker, Wen Li, Craig W. Hogle, Vandana Sharma, Xibin Zhou, Henry C. Kapteyn, Margaret M. Murnane, Andreas Becker Imaging and controlling reactions in molecules and materials at the level of electrons is a grand challenge in physics and chemistry. Using reaction microscope techniques along with calculations using the strong-field approximation, we show that we can capture the entire valence shell electron density in a molecule as a molecular bond breaks. To this end, we use an intense ultrashort laser pulse to ionize a Bromine molecule at different times during dissociation. The total ionization signal and the angular distribution of the ion yields is observed. Our results show that both signals vary strongly over a surprisingly long time after the start of the dissociation process. [Preview Abstract] |
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L1.00138: Double core-hole electron spectroscopy of formamide Steve Southworth, Gilles Doumy, Dipanwita Ray, Elliot Kanter, Bertold Kraessig, Yuelin Li, Linda Young, Jochen Kuepper, John Bozek, Christoph Bostedt, Marc Messerschmidt, Nora Berrah, Li Fang, Brendan Murphy, Timur Osipov, James Cryan, James Glownia, Shambhu Ghimire, Nikolai Kryzhevoi, Lorenz Cederbaum, Robin Santra The intense, femtosecond x-ray pulses generated at the Linac Coherent Light Source can produce double core-holes (DCH) by absorbing two photons sequentially prior to Auger decay [1,2]. DCH binding energies at different atomic sites are sensitive to the chemical environment and electron correlations. DCH features appear in photoelectron and Auger electron spectra. At the LCLS, we used 1000 - 1200 eV x-rays with estimated pulse durations $<$ 10 fs to record electron spectra of formamide, HCONH$_{2}$. The measured electron spectra are compared with calculated DCH binding energies at the C, O, and N sites of the molecule. [1] R. Santra \textit{et al.}, Phys. Rev. Lett. \textbf{103}, 013002 (2009). [2] L. Fang \textit{et al}., Phys. Rev. Lett. \textbf{105}, 083005 (2010). [Preview Abstract] |
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L1.00139: Dissociative Photoionization of Methane at the Carbon K-edge J.B. Williams, A.L. Landers, C. Trevisan, I. Bocharova, F. Sturm, C.W. McCurdy, A. Belkacem, Th. Weber, T. Jahnke, M.S. Schoeffler, R. Doerner We have used Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) to measure the momenta of the photoelectron and the molecular fragments arising from the dissociation of the methane molecule following Auger decay. Methane is one of the simplest 3-dimensional polyatomic molecules and provides a testing ground to study the interplay between the electronic and the nuclear motion. Soft X-ray radiation from the Advanced Light Source (ALS) at LBNL was used to core-ionize the methane. One decay pathway resulting from this breakup is C(1s$^{-1})$H$_{4}^{+\ast }$+ e$^{-}_{\gamma }\to $ CH$_{3}^{+}$ + H$^{+}$ + e$^{-}_{\gamma }$ + e$^{-}_{auger}$. In this channel we are able to determine the orientation of the bond axis (between the CH$_{3}^{+}$ and H$^{+}$ ions) using the axial recoil approximation; the result is an azimuthally symmetric Molecular Frame Photoelectron Angular Distribution (MFPAD). We are also examining the different accessible vibrational modes to see if there are correlated changes in the MFPADs and fragmentation branching ratios, as well as exploring the use of three-fragment dissociation to fully orient the molecule. The preliminary results of the experiment will be presented and compared to a preliminary theoretical calculation of the MFPADs for methane. [Preview Abstract] |
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L1.00140: Thomson-resonant interference effects in quasielastic x-ray Raman scattering near the Cl K edge of HCl Dennis W. Lindle, Stephane Carniato, Patricia Selles, Loic Jounel, Renaud Guillemin, Wayne C. Stolte, Lara El Khoury, T. Marin, Faris Gel'mukhanov, Marc Simon Quasielastic x-ray Raman scattering is investigated experimentally and theoretically around the Cl K edge of HCl. Strong interference effects between Thomson scattering and resonant scattering are observed throughout the near-threshold region, where the Thomson and resonant scattering contributions are found to be of comparable strength, a result in contrast to the conventional wisdom about the importance of nonresonant scattering. The results also exhibit strong polarization sensitivity, allowing easy identification of interferences between resonant and nonresonant channels. [Preview Abstract] |
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L1.00141: Photo-multidetachment and Fragmentation of C$_{60}^-$ R.C. Bilodeau, M. Hoener, N. Berrah, S. Schippers, A. M\"{u}ller, D.A. Esteves, R. Phaneuf, N.D. Gibson, C.W. Walter, A. Aguilar, J.M. Rost Absolute single-photon multi-detachment and fragmentation cross sections of C$_{60}^-$ fullerene anions have been measured as a function of energy with the merged ion-photon beam apparatus at the ALS. Multiple electron ejection was substantial at all photon energies, allowing product charge states up to C$_{60}^{3+}$ to be measured. We argue that $q$-fold detachment spectra of C$_{60}^-$ relate directly to $q$-fold ionization of neutral C$_{60}$, except the loosely bound excess electron of C$_{60}^-$ results in a significant change of the energy scale and increase of the absolute cross section, with otherwise little change in the structure. Fragmentation into cations of C$_{58}$ and C$_{56}$ was also studied. We conclude from the determination of appearance thresholds that fragmentation occurs at significantly lower photoexcitation energies in C$_{60}^-$ than in C$_{60}$. [Preview Abstract] |
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L1.00142: Experimental evidence of confinement resonances in the photoionisation of the endohedral Xe@C$_{60}^{+}$ D. Kilcoyne, A. Aguilar, A. M\"{U}ller, S. Schippers, C. Cisneros, G. Alna'Washi, N. Aryal, K. Baral, D. Esteves, C. Thomas, R. Phaneuf A recent communication [1] presented experimental evidence of confinement resonances associated with the photoabsorption by a noble gas atom in a C$_{60}$ cage. The giant 4d resonance in the photoionization of Xe is predicted to be modulated into four components when the Xe atom is confined within C$_{60}$ due to multi-path interference of photoelectron waves caused by reflection from the C$_{60}$ cage. The measurements were performed in the photon energy range 60 - 150 eV by merging a beam of synchrotron radiation with a mass/charge selected ion beam current at a fraction of a picoampere, of the endohedral. The phenomenon was observed in the cross section for double photoionization of Xe@C$_{60}^+$ accompanied by fragmentation of two carbon atoms, yielding Xe@C$_{58}^{3+}$ product ions. This research was supported by the Division of Chemical Sciences, Geosciences and Biosciences of the U.S. Department of Energy, the Deutsche Forschungsgemenischaft, Germany and CONACYT-82521, M\'{e}xico.[1] A.L.D. Kilcoyne et al., Phys. Rev. Lett. 105, 213001 (2010) [Preview Abstract] |
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L1.00143: Femtosecond Dynamics of Non-Resonant Dissociative Ionization Roy Anunciado, Lutz Huwel With the aid of molecular beam and a linear time-of-flight (TOF) spectrometer, we have studied Na$^{+}$ production in non-resonant multi-photon ionization of Na$_{2}$ using 355 nm and 532 nm photons. Flight time spectra reveal several processes from our spectra with photo-fragment energies of Na$^{+}$ ranging from 0-1.32eV. Three processes were identified: (i) 3-photon ionization followed by 1-photon dissociation; (ii) 2-photon dissociative excitation followed by 1-photon ionization of electronically excited fragments (4s, 3d, 4p), and (iii) dissociative autoionization along doubly excited state converging to the repulsive 1$^{2}\sum _{u}^{+}$ state of Na$_{2}^{+}$. Dynamics in case (iii) involves competition between electronic (autoionizing) and nuclear (dissociative) degrees of freedom. We were able to generate model Rydberg potential curves and utilize it in our simulation to fit our experimental data since the shape of these Rydberg potentials are not known. Position dependent autoionization lifetimes, 1/ $\Gamma $(R), are parametrically incorporated in our model, as are appropriate fragment angular distributions\footnote{Dixon, R., J.Chem.Phys. 122, 194302 (2005)} for the various processes, and laser polarization and power dependence. Results of our modeling based on our analysis and experimental approach will be presented. [Preview Abstract] |
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L1.00144: Angular Dependance of Auger electrons from N$_{2}$ James Cryan, James Glownia, N.A. Cherepkov, P.H. Bucksbaum, R.N. Coffee One of the primary goals for x-ray free electron lasers (xFELs) is the study of x-ray interactions in the molecular-frame. Impulsive molecular alignment can be used to bring the molecular frame into the laboratory frame without perturbing the electronic states. We present molecular frame Auger electron spectra corresponding to quasi-bound final states of N$_{2}^{2+}$. We compare experimental and calculated angular distributions of Auger electrons and find good qualitative agreement. These and potential future measurements could lift ambiguity in previous $KLL$-Auger energy assignments. [Preview Abstract] |
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L1.00145: ABSTRACT WITHDRAWN |
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L1.00146: Double ionization of O$_{2}$ via single photon at energy below double ionization threshold I.A. Bocharova, C. Stuck, M. Schoeffler, A. Belkacem, Th. Weber, R. Doerner, T. Jahnke, A. Landers, C.L. Cocke We studied the double ionization of O$_{2}$ molecule at photon energies below the double ionization threshold (about 41.5 eV). At this energy the double ionization is a two-step process. A highly excited cation state is produced by the interaction of the neutral molecule with the photon. The cation autoionizes subsequently. We try to elucidate the dissociative intermediate states of this singly charged ion during this double ionization processes. Therefore we performed a kinematically complete experiment measuring the 3d-momentum vectors of two electrons and two oxygen ions in coincidence following the excitation of O$_{2}$, dissociation of O$_{2}^{+}$ and the subsequent autoionization of the excited neutral oxygen atom. We present the ionic kinetic energy release as a function of electron energies (energy maps), electron angular distributions in the body fixed frame and compare our results to previous time-resolved studies [A. Sandhu et al., Science, 322, 1081, (2008)]. [Preview Abstract] |
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L1.00147: Dielectric response effects in time-resolved photoemission from metal surfaces Chang-hua Zhang, Uwe Thumm We investigate dielectric response effects in attosecond time-resolved photoelectron (PE) spectra from metal surfaces [1]. We model the response of the metal due to excitation of bulk and surface plasmons by the creation and propagation of the PE in terms of an effective potential that depends on the velocity of the PE. Using this dynamical image potential, we calculate IR-streaked XUV-photoemission spectra and compare them with spectra obtained with the corresponding {\em static} image potential. We find a significant relative temporal shift [2] in photoemission from the conduction band for calculations with static and dynamical image potentials. We further analyze the dependence of this relative shift on the XUV frequency as well as on solid-state characteristics, such as the bulk plasmon frequency, the IR skin depth, and the PE transport in the solid [3]. \\[4pt] [1] C.-H. Zhang and U. Thumm, Phys. Rev. Lett. 102, 123601 (2009); Phys. Rev. A 80, 032902 (2009).\\[0pt] [2] C.-H. Zhang and U. Thumm, Phys. Rev. A 82, 043405 (2010).\\[0pt] [3] C.-H. Zhang and U. Thumm, Dielectric response effects in attosecond time-resolved streaked photoelectron spectra of metal surfaces, submitted. [Preview Abstract] |
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L1.00148: Monochromatic X-Ray Irradiation of High-Z Atoms and Nanoparticles for Biomedical Applications Sara Lim, A. Pradhan, S. Nahar, E. Chowdhury, Y. Yu, K. Huang, K. Yan We will report theoeretical and experimental studies of resonant X-ray interaction with heavy elements for potential applications to cancer diagnsotics and therapy. The resonant transitions may be targeted with monochromatic X-ray sources, such as synchrotron photon beams and high-intensity pulsed lasers [1] following a deep inner-shell ionization. X-rays from conventional machines in medical use are broadband with filtered bremsstrahlung spectrum. This is very ineffcient as low-energy X-rays are absorbed without much penetration and high-energy x-rays pass through without much interaction. Calculations of Auger cascades and K-shell resonance positions [2] show that monochromatic beams may be employed to optimize localized energy deposition in high-Z nanomaterials embedded, e.g. in a cancerous tumor. Theoretical results for several elements from bromine (Z = 35) to gold (Z = 79) and experimental studies for partial conversion of bremsstrahlung spectrum from conventional X-ray sources into K-alpha radiation for imaging and/or therapeutics will be reported.\\[4pt] [1] Pradhan et al., J. Phys. Chem. A 113, 12356 (2009);\\[0pt] [2] Nahar et al. Can. J. Phys. (in press)- Partial Support: DOE [Preview Abstract] |
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L1.00149: Plasma generation by chirped ultrashort laser pulses Jeremy Gulley Current models of ultrafast-laser induced ionization in dielectric materials typically assume that the ultrashort pulse is (at least approximately) monochromatic. However, in recent years it has been demonstrated both computationally and experimentally that material damage by ultrashort laser pulses significantly depends on the chirp of the pulse in question. Here we present results from a recent study that explores this problem using simulations of laser-induced ionization in dielectrics where free-carrier generation is sensitive to the instantaneous frequency of the laser pulse. It is demonstrated that plasma generation by initially unchirped pulses is not immune from this chirp-dependence since nonlinear optical effects, such as super-continuum generation, significantly chirp the pulse as it propagates. [Preview Abstract] |
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L1.00150: Numerical study of Penning-Malmberg-Surko positron trap efficiency Srdjan Marjanovic, Milovan Suvakov, Ana Bankovic, Zoran Lj. Petrovic Efficiency of a gas filled positron trap can be improved in two ways: by shortening the operation time required to thermalize the particles in the trap, and by increasing the percentage of particles trapped. We examine both techniques by a well tested Monte Carlo code, and give an overview of the loss processes involved. Temporal and spatial evolution of the energy distribution of particles allows us to show gradual transition of a beam into a swarm of particles. The model trap is a classic three stage potential well design using N$_{2}$ as a buffer gas in the first two stages and a N$_{2}$/CF$_{4}$ mixture in the third. It was found that including cross sections for rotational e$^{+}$-N$_{2}$ excitation is essential to achieve final stages of thermalization. Various trap implementations use different sources and moderators, and depending on the properties of the incoming beam, the trap itself can be optimized by changing its attributes (buffer gas pressures, dimensions of the chamber, electric potential shape, duration of different operation stages, etc.) [Preview Abstract] |
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L1.00151: ABSTRACT WITHDRAWN |
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L1.00152: Highly Charged Ion-induced fragmentation of water in all its forms L. Adoui, R. Maisonny, S. Legendre, M. Capron, J.Y. Chesnel, A. Domaracka, B. Manil, A. Mery, J. Rangama, J.C. Poully, P. Rousseau, B.A. Huber, B. Gervais, E. Giglio, M.F. Politis, M.A. Herve du Penhoat, M.P. Gaigeot, P. Lopez-Tarifa, M. Alcami, F. Martin Understanding of the molecular bond breakage selectivity, in order to control the bond cleavage, is one of the most exciting challenges in chemistry. The isotopomer of water HOD provides a three--atom prototype for studying such bond selectivity. A strong isotopic effect is evidenced in HOD$^{2+}$ ion fragmentation [1-2]. Moreover, the current interest in describing the biological radiation damage \textit{at the molecular level} has triggered the investigation of dissociation of water molecules in highly ionizing collisions. In order to bridge the gap between molecules and liquid medium, we investigate the stability of water clusters as they have been suggested to participate in many chemical and physical processes [3]. A strong evolution from a partial dissociation to a full explosion of the cluster has been evidenced when the charge state of low energy ions is increased [4]. Perspectives will also be discussed. [1] J.Phys.B \textbf{38} (2005) L233; [2] J.Chem. Phys. \textbf{131 }(2009) 024302; [3] J.Phys.B:. \textbf{42} (2009) 075101; [4] Phys Rev A (2011) [Preview Abstract] |
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L1.00153: FUNDAMENTAL SYMMETRIES AND PRECISION MEASUREMENTS |
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L1.00154: ABSTRACT WITHDRAWN |
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L1.00155: Do Photons Have Rest Mass? Probably Not, But... Dallin Durfee, Christopher Erickson, James Archibald I will discuss the possibility of setting new laboratory-based limits on the rest mass of the photon and deviations from Coulomb's inverse-square law. Consequences of a non-zero photon rest mass will be discussed, and the Proca theory of massive photons will be applied to a potential ion interferometer experiment. The results show that, given reasonable experimental parameters, a table-top experiment could result in improvements on laboratory-based limits by two orders of magnitude. [Preview Abstract] |
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L1.00156: Optical excitation and decay dynamics of ytterbium atoms embedded in solid neon matrix Chen-Yu Xu, Shuiming Hu, Kevin Bailey, Zheng-Tian Lu, Peter Mueller, Thomas O'Connor, Jaideep Singh We have studied the optical excitation and decay dynamics of neutral ytterbium atoms embedded in cryogenic solid neon. The embedded atoms qualitatively retain the structure and transition property of free atoms in the gas phase. The transitions are shifted by and broadened to typically a few hundred cm$^{-1}$. The broadening mechanism is found to be homogeneous. Atomic population can be transferred among the internal levels via resonant optical excitation and spontaneous decay. The rates of intercombination transitions between spin-singlet and spin-triplet levels are vastly enhanced, probably due to strong Stark-induced mixing. However, the 6s6p 3P0 level is found to remain metastable, with its lifetime determined to be 14 s for the odd isotopes and a few minutes for the even isotopes. This work is supported by DOE, Office of Nuclear Physics, under contract DEAC02-06CH11357. [Preview Abstract] |
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L1.00157: High-precision study of Hg$^+$ atomic properties Matt Simmons, M.S. Safronova, U.I. Safronova The systematic study of Hg$^+$ properties is carried out using high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Third-order many-body perturbation theory calculations are also carried out to establish the size of the higher-order corrections. Excitation energies of the [Xe]$4f^{14}5d^{10}ns$, [Xe]$4f^{14}5d^{10}np$, [Xe]$4f^{14}5d^{10}nd$, [Xe]$4f^{14}5d^{10}n'f$, and [Xe]$4f^{14}5d^{10}n'g$ ($n \leq$ 10, $n' \leq$ 9) states in Hg$^+$ are evaluated. Reduced matrix elements, oscillator strengths, and transition rates are determined for electric-dipole transitions including the $ns$ ($n=6-11$), $np$ ($n=6-10$), $nd$ ($n=6-10$), $nf$ ($n=5-9$), and $ng$ ($n=5-9$) states. Lifetimes of these states, E1 ground state polarizability, and the hyperfine $A$ and $B$ constants of the first low-lying levels up to $n$ = 7 are determined. The quadratic Stark effect on hyperfine structure levels of $^{199}$Hg$^+$ ground state is investigated. These calculations provide critically evaluated recommended values of Hg$^+$ atomic properties. [Preview Abstract] |
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L1.00158: Microwave Cavity for Anapole Moment Measurement in Francium Jiehang Zhang, Dong Sheng, Luis Orozco We present a study of the Polka-Dot microwave plano-spherical mirror for a Fabry-Perot resonator. The microwave resonator is an essential element of the apparatus to measure the anapole moment in francium. A crucial requirement for the cavity is the mode-matching into the fundamental Gaussian TEM$_{00}$ mode. We investigate new coupling mechanisms of the radiation into the cavity to suppress unwanted higher order modes. We are exploring the method of printing two dimensional array of holes and feeding in through horn antennas. According to a HFSS simulation, this method should improve significantly the mode purity in contrast to conventional antenna. We fabricate the mirrors on standard optical blank using standard film deposition techniques with lithographic method to print the pattern. Preliminary tests show resonances, with potential improvements of the Q factors. [Preview Abstract] |
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L1.00159: Precise measurement of the Stark shift within the 5P$_{1/2}$$\rightarrow$6S$_{1/2}$ transition in $^{115}$In A.T. Lorenzo, G. Ranjit, P.K. Majumder We are pursuing a series of precise atomic structure measurements in Group IIIA elements---currently thallium and indium---designed to test recent ab initio theoretical calculations in these systems. In indium, a two-step, two-color vapor cell hyperfine spectroscopy experiment was recently completed in our laboratory. Previously, an atomic beam system in conjunction with a thallium oven source and high-voltage field plates was used to complete a precise scalar polarizability measurement in thallium. In our current work, we have designed a new indium atomic beam source, and are pursuing a precision measurement of the indium atomic polarizability within the 410 nm 5P$_{1/2}$$\rightarrow$6S$_{1/2}$ transition. The new source is capable of reaching 1100 $^{\circ}$C and contains a series of parallel effusive slits to produce a dense, collimated beam of indium. We intersect the laser transversely with the atomic beam in the presence of a precisely calibrated electric field of 30 kV/cm. Frequency modulation of the laser, and simultaneous piezoelectric modulation of the atomic beam allows a dual-frequency lock-in detection scheme. This produces a zero-background atomic absorption spectrum of high signal-to-noise ratio. Our goal is to achieve a polarizability measurement at the 1{\%} level of accuracy or better, which will provide a stringent new test of the atomic theory calculations. [Preview Abstract] |
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L1.00160: Resolved atomic interaction sidebands in an optical clock transition Ana Maria Rey, Michael Bishof, Yige Lin, Matthew Swallows, Michael Martin, Alexey Gorshkov, Jun Ye We report the observation of resolved atomic interaction sidebands (ISB) in the $^{87}$Sr optical clock transition when atoms at microkelvin temperatures are confined in a two-dimensional (2D) optical lattice. The ISB are a manifestation of the strong interactions that occur between atoms confined in a quasi-one-dimensional geometry and disappear when the confinement is relaxed along one dimension. The emergence of ISB is linked to the recently observed suppression of collisional frequency shifts [1]. At the current temperatures, the ISB can be resolved but are broad. At lower temperatures, ISB are predicted to be substantially narrower and usable as powerful spectroscopic tools in strongly interacting alkaline earth gases. \\[4pt] [1] M. D. Swallows \textit{et al}. Science (10.1126/science.1196442.) [Preview Abstract] |
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L1.00161: High Accuracy Characterization of an Astro-comb with an FTS Alex Glenday, Chih-Hao Li, David Phillips, Sylvain Korzennik, Guoqing Noah Chang, Li-Jin Chen, Andrew Benedick, Franz Kaertner, Dimitar Sasselov, Andrew Szentgyorgyi, Ronald Walsworth Searches for extrasolar planets using the periodic Doppler shift of stellar lines are approaching Earth-like planet sensitivity. To find a 1-Earth-mass planet in an Earth-like orbit, an order of magnitude improvement in state-of-the-art radial velocity spectroscopy is necessary. An astro-comb, the combination of an ocatve-spanning laser frequency comb with a Fabry-Perot cavity, producing evenly spaced frequency markers with the potential for large wavelength coverage is a promising avenue towards improved wavelength calibration. Key to achieving high accuracy and long-term stability of the astro-comb is high-quality suppression of undesired comb laser lines by the Fabry-Perot filter cavity. Here we present a characterization of a green astro-comb produced by broadening a Ti:Sapphire laser using photonic crystal fiber (PCF) and filtered through zero group delay dispersion mirror sets optimized for the green. The characterization is performed using a high-resolution FTS constructed in our laboratory. [Preview Abstract] |
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L1.00162: Red, Green, and Blue Astro-combs David Phillips, Alex Glenday, Chih-Hao Li, Sylvain Korzennik, Guoqing Noah Chang, Li-Jin Chen, Andrew Benedick, Franz Kaertner, Dimitar Sasselov, Andrew Szentgyorgyi, Ronald Walsworth Searches for extrasolar planets using the periodic Doppler shift of stellar lines are approaching Earth-like planet sensitivity. Astro-combs, a combination of an octave spanning femtosecond laser and a mode-filtering cavity provide a likely route to increased calibration precision and accuracy. We present results from three astro-combs operating in the red/near-IR, green and blue spectral ranges. Light from a 1-GHz, octave-spanning Ti:Sapphire laser is filtered by a Fabry-Perot Cavity (FPC) constructed from Doubly-Chirped Mirrors to produce a red astro-comb with 100 nm of optical bandwidth. This astro-comb has calibrated an astrophysical spectrograph at the 1 m/s level. In the blue astro-comb, Ti:Sapphire comb light, doubled in a BBO crystal is filtered to 50 GHz mode spacing with an FPC. The blue astro-comb has performed 50 cm/s calibrations. In the ``green'' astro-comb, light from the 1 GHz Ti:Sapphire comb laser is broadened in a photonic crystal fiber optimized to produce light in the green. This 1-GHz spaced green light is then filtered to roughly 40 GHz via an FPC with zero group delay dispersion mirrors, providing approximately 50 nm of astro-comb light centered near 550 nm. [Preview Abstract] |
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L1.00163: Towards the next decades of precision and accuracy in a $^{87}$Sr optical lattice clock Michael Martin, Yige Lin, Matthew Swallows, Michael Bishof, Sebastian Blatt, Craig Benko, Licheng Chen, Takako Hirokawa, Ana Maria Rey, Jun Ye Optical lattice clocks based on ensembles of neutral atoms have the potential to operate at the highest levels of stability due to the parallel interrogation of many atoms. However, the control of systematic shifts in these systems is correspondingly difficult due to potential collisional atomic interactions. By tightly confining samples of ultracold fermionic $^{87}$Sr atoms in a two-dimensional optical lattice, as opposed to the conventional one-dimensional geometry, we increase the collisional interaction energy to be the largest relevant energy scale, thus entering the strongly interacting regime of clock operation. We show both theoretically and experimentally that this increase in interaction energy results in a paradoxical decrease in the collisional shift, reducing this key systematic to the $10^{-17}$ level.\footnote{M~D.~Swallows \textit{et al.} Science, 10.1126/science.1196442, 2011} We also present work towards next- generation ultrastable lasers to attain quantum-limited clock operation, potentially enhancing clock precision by an order of magnitude. [Preview Abstract] |
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L1.00164: Progress towards a nuclear EDM measurement of Ra-225 Jaideep Singh, M.R. Dietrich, M. Kalita, R.H. Parker, I.A. Sulai, K. Bailey, J.P. Greene, P. Mueller, T.P. O'Connor, R.J. Holt, Z.-T. Lu We are developing a long term program to search for the permanent electric dipole moment (EDM) of the Radium-225 nucleus. A nonzero nuclear EDM is a signature of of $CP$- and $T$-violating interactions within nuclei. Currently, the best experimental limits on these interactions are derived from EDM measurements of Mercury-199. The Ra-225 radioisotope (half-life of 15 days) is an attractive alternative because, due to its peculiar shape (octupole deformation), it is predicted to be $10^2$-$10^3$ times more sensitive to these types of interactions than Hg-199. In our measurement scheme, Ra atoms are first laser cooled \& trapped in a magneto-optical trap (MOT) and then transferred to an optical dipole trap (ODT), both of which have already been demonstrated. Currently being studied is the motion of this ODT into the science chamber and the transfer of atoms into a second ODT. We will report on progress towards measurements of atomic properties necessary for the EDM search and the EDM search itself. [Preview Abstract] |
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L1.00165: Progress towards a permanent electron electric dipole moment search using cold atoms in an optical lattice Neal E. Solmeyer, Kunyan Zhu, David S. Weiss Observation of a permanent electric dipole moment of the electron would imply CP violating effects not contained in the Standard Model. We present our progress towards measuring the electron EDM using laser-cooled cesium and rubidium atoms trapped in a one dimensional optical lattice. We have collected Cs atoms in a MOT and have launched them 90 cm vertically using two cavity-enhanced optical lattice guides. In that region, which is suitable for measurement, we re-cooled and re-trapped the atoms with an overall transfer efficiency from the MOT of 50\%. The two 1D lattice traps thread through three specially-coated glass electric field plates. Very low frequency Ramsey-like spectroscopy will be sensitive to an EDM with an ultimate precision of $3\times10^{-30}$ e-cm. [Preview Abstract] |
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L1.00166: Progress Toward an Improved Electron g-factor Measurement J.C. Dorr, S. Fogwell Hoogerheide, G. Gabrielse The electron g-factor measurement, combined with an independent determination of the fine structure constant, can be used to make the most precise test of quantum electrodynamics (QED). Alternatively, the g-factor measurement can make the most accurate determination of the fine structure constant, if QED is assumed to be valid. The electron g-factor is also key in providing the tightest bound for CPT violation for leptons by comparing the electron and positron g-factors. The previous measurement of the electron g-factor was made with a precision of 0.28 parts per trillion on a single quantum oscillator in a cylindrical penning trap at 100 mK.\footnote{D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett. 100, 120801 (2008).} The uncertainty in the measurement was dominated by lineshape uncertainty. Here we report progress toward an improved electron (and an initial positron) g-factor measurement in a new high stability apparatus within an improved penning trap. These measurements would improve the determination of the fine structure constant and set a new bound on CPT violation in a lepton system. [Preview Abstract] |
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L1.00167: Progress towards laser-controlled formation of antihydrogen in a Penning-Ioffe trap Robert McConnell The recent announcement of trapped antihydrogen ($\bar{H}$) [1] opens the door to precise tests of CPT symmetry via spectroscopic comparison of magnetically confined atoms and anti-atoms. An important challenge is to trap sufficient numbers of $\bar{H}$ atoms to allow high-precision spectroscopy. Laser-controlled charge-exchange has been shown to be an efficient method of producing $\bar{H}$ [2]. Laser-controlled charge exchange allows large numbers of positrons ($e^+$) to be used in the $\bar{H}$ formation process and should produce atoms with speeds given by the initial thermal velocities of the antiprotons ($\bar{p}$) involved, which may be adiabatically cooled to 3.5 K or below [3]. We report progress towards the laser-controlled formation and trapping of $\bar{H}$ in a Penning-Ioffe trap. A Rydberg \emph{Cs} beam charge-exchanges with trapped $e^+$ to produce metastable \emph{Ps*} atoms which undergo a second charge-exchange and produce $\bar{H}$. As many as 3,600 $\pm$ 600 $\bar{H}$ atoms per trial are likely being produced by this method, a 100-fold increase over previous efforts, although some outlying difficulties in the detection process remain. Experiments towards trapping $\bar{H}$ produced by this method are underway. [1]. G. B. Andresen et al. (ALPHA Collaboration), Nature (London) 468, 673 (2010). [2]. C. H. Storry, et al. (ATRAP Collaboration), Phys. Rev. Lett. 93, 263401 (2004). [3] G. Gabrielse, et al. (ATRAP Collaboration), Phys. Rev. Lett. (in press). [Preview Abstract] |
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L1.00168: Precision Atomic Masses of Strontium and Ytterbium Raman Rana, Andrew Zarrella, Edmund Myers Currently the second most precise value for the fine structure constant is derived from ``photon-recoil'' measurements of \textit{h/M(Rb)} combined with measurements of the Rydberg constant, atomic transition frequencies, and atomic masses of the electron and Rubidium. An improved value for alpha using this method will enable the combination of theory and experiment for the $g-$factor of the electron, which produces the most precise value for alpha, to provide a further improved test of QED. Besides the alkalis, isotopes of Sr and Yb make promising candidates for photon-recoil measurements of \textit{h/M(atom).} Using single-ion, cryogenic precision Penning trap techniques, we are measuring their atomic masses with the aim of a precision of 0.1ppb, a factor of 100 or more improvement over current values. [Preview Abstract] |
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L1.00169: Atomic polarisabilities, hyperpolarisabilities and the factorisation of molecular interactions J.M. Rossi, B.A. Rigsbee, K.G. Rollin, M.W.J. Bromley, Jim Mitroy The properties of one and two-electron atoms and their molecules are calculated numerically using configuration interaction and perturbative methods. Firstly, we present calculations of the dynamic dipole and hyperpolarisabilities of the ground and low-lying excited states of atoms emphasising low-energy fields of interest in atomic clocks, and high-energy excitations that probe near Rydberg states. Theoretical expressions will be presented that factorise the long-range dispersion forces between two atoms into their individual scalar and tensor dipole polarisabilities at imaginary frequencies. This method yields $C_6$ dispersion coefficients in agreement with the latest theoretical values for both homo-nuclear and the hetero-nuclear interactions, eg. Li($2s$)-H($1s$). The application of this methodology to di-atomic molecular symmetries involving non-$s$-wave atomic states will be emphasised. [Preview Abstract] |
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L1.00170: Evaluation of a possible optical e-EDM measurement Haoquan Fan, James Coker, Tao Zh. Yang, Jerry Gillean, N.E. Shafer-Ray Since its proposed existence by Purcell and Ramsey in 1950, the possibility of an electron electric dipole moment (e-EDM) has been the subject of extensive theoretical and experimental investigation. Here we describe an ongoing effort to probe for an e-EDM by measuring the energy difference between two states of the PbF molecule that differ only by their orientation with respect to an applied external electric field. Specifically, we describe a possible optical Ramsey resonance experiment utilizing rotating linearly polarized light. We present initial tests of this scheme, including measurement of a small angle of rotation of a polarized beam splitter and measurement of optical Stark spectroscopy of the PbF molecule. We discuss these results and the limitations they place on a measurement of an e-EDM. [Preview Abstract] |
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L1.00171: A K-Rb-$^{21}$Ne Comagnetometer for Tests of Fundamental Symmetries and Inertial Rotation Sensing Justin Brown, Marc Smiciklas, Lawrence Cheuk, Michael Romalis The K-$^3$He noble gas comagnetometer has already set the most stringent limit on possible Lorentz and CPT violation coupling to nuclear spin and on long-range nuclear spin-dependant forces. The comagnetometer is mounted on a rotating platform for reorientation of the sensitive axis in the horizontal plane that is a key to improved tests of spatial isotropy. Replacement of $^3$He with $^{21}$Ne provides an order of magnitude improvement in sensitivity to non-magnetic nuclear spin interactions due the smaller gyromagnetic ratio of $^{21}$Ne. Because $^{21}$Ne has $I=3/2$, the experiment is also sensitive to tensor Lorentz-violating effects that do not break CPT symmetry. The comagnetometer also works as a sensitive gyroscope that is potentially competitive with fiber-optic and atomic Sagnac interferometers. We will describe our current development of the K-Rb-$^{21}$Ne comagnetometer as a gyroscope and a precision measurement tool. Finally, we discuss the advantage and future plans for Lorentz Violation tests at the South Pole for removal of Earth's rotation rate as a background systematic effect. [Preview Abstract] |
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L1.00172: Shifts from a distant neighboring resonance E.A. Hessels, M. Horbatsch The linecenter of a resonance is affected by the presence of neighboring resonances due to quantum interference between the two resonant processes. Such shifts must be accounted for in high-precision measurements, but are easily overlooked. We develop an analytic formulation for the effect in the simplest case of a three-level atom. The shifts in this model system are large enough to be of concern for precision measurements. [Preview Abstract] |
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L1.00173: Dispersion Tuned Spectroscopy of Te$_{2}$ James Coker, Neil Shafer-Ray, Tao Zh. Yang, Haoquan Fan We present saturation absorption spectroscopy of the X$_{1}(^{3}\Sigma _{g})$ - B($^{3}\Sigma _{u})$ transition in Te$_{2}$. This spectra was taken using a blue diode laser locked to a Fabry Perot cavity that is in turn locked to a Zeeman stabilized Helium Neon laser. Tuning of the diode laser frequency is accomplished by CO$_{2}$ pressure tuning the Fabry Perot cavity. The result is a tuning frequency that is proportional to the dispersion of the index of refraction between the Helium Neon and diode laser wavelengths. We discuss the stability of the laser frequency when the CO$_{2}$ pressure is tuned to the center of a Te$_{2}$ absorption line. This work is motivated by ongoing efforts to measure the electrons electric dipole moment and, more specifically, our desire to produce a frequency locked source of radiation for use in detection of the PbF molecule. [Preview Abstract] |
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L1.00174: Towards a Measurement of the Nuclear Magnetic Octupole Moment of $^{137}$Ba Matthew Hoffman, Adam Kleczewski, Eric Magnuson, E.N. Fortson, Boris Blinov Measurements of hyperfine structure in a $^{133}$Cs atom resolved a nuclear magnetic octupole moment, $\Omega$, much larger than expected.\footnote{V. Gerginov, A. Derevianko, and C. E. Tanner, Phys. Rev. Lett. 91, 072501} To explore this anomaly further, we are undertaking an experiment to measure the hyperfine structure of the 5D levels of $^{137}$Ba. We will selectively populate the m=0 states in the 5D$_{3/2}$ manifold by driving the 6S$_{1/2}$ to 5D$_{3/2}$ electric quadrupole transition using a commercially available Tm,Ho:YLF laser. Using the Pound-Drever-Hall frequency stabilization method we locked this laser to a high finesse cavity made of ULE glass and demonstrated a laser linewidth of less than 750 Hz. Once the barium ion is initialized to an m=0 state of a chosen 5D$_{3/2}$ hyperfine sublevel, we will perform RF spectroscopy to measure the hyperfine splittings with mHz precision. A measurement the 5D$_{3/2}$ hyperfine intervals combined with a similar measurement of the 5D$_{5/2}$ hyperfine intervals (using a 1762 nm fiber laser) will allow theorists to extract a value for $\Omega$. [Preview Abstract] |
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