Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session M6: Poster Session III |
Hide Abstracts |
Room: Burnham Yates Conference Center Lancaster 4:00-5:30 pm |
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M6.00001: ULTRACOLD COLLISIONS AND PHOTOASSOCIATION PROC II
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M6.00002: Ultracold Mixture: Molecule Production in K-40 and Rb-87 Joshua Zirbel, Kang-Kuen Ni, Deborah Jin, Carl Wieman We report on a new apparatus for making ultracold heteronuclear molecules. Large numbers of fermionic $^{40}$K (1*10$^{8 }$atoms) and bosonic $^{87}$Rb (5*10$^{8 }$atoms) have been collected simultaneously. The mixed sample can then be loaded into a magnetic trap and physically moved to a lower pressure, science region. A novel feature of this transfer is the navigation around an obstruction made of pyrex. The purpose of this obstruction is to block line-of-sight atoms from migrating to the low pressure section but still allow for optical probing along the transfer direction. A QUIC Ioffe-Pritchard style magnetic trap is used to hold the mixture during (sympathetic) cooling. Progress towards quantum degeneracy in the mixed samples and recent work will also be reported. [Preview Abstract] |
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M6.00003: Heteronuclear Feshbach Resonances in a Bose-Fermi Mixture of 40K and 87Rb M. L. Olsen, J. Goldwin, S. Inouye, J. Lang, D. S. Jin We have observed four magnetically tunable heteronuclear Feshbach resonances between fermionic 40K and bosonic 87Rb. Comparison of the measured positions of the resonances with theory identifies three as s-wave resonances and one as a p-wave resonance. We report on studies of inelastic loss of the mixture at these resonances. The observation of these resonances has allowed for a more precise determination of the background Rb-K interspecies scattering length. [Preview Abstract] |
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M6.00004: Associative and Penning Ionization in a Rb MOT Mark Trachy, Howard Camp, Mudessar Shah, Brett DePaola, Alina Gearba Two important loss mechanisms in magneto-optical traps containing excited species are associative and Penning ionization. In a trap containing a mixture of Rb(5s), Rb(5p) and Rb(4d) atoms, a prodigious quantity of ions are produced from the following reactions: \[ \begin{array}{l} Rb(5p)+Rb(4d)\to Rb_2^+ +e^- \\ Rb(4d)+Rb(4d)\to Rb_2^+ +e^- \\ \quad \quad {\kern 1pt}\quad \quad \quad \;\;\quad \to Rb(5s)+Rb^++e^-. \\ \end{array} \] Ionizing collisions involving only Rb(5p) are energetically not allowed in the low temperature MOT environment. By measuring the flight times of the ions extracted from the MOT, we deduce the relative cross sections for the production of ionic dimers and monomers. By additionally measuring the relative populations of Rb(5p) and Rb(4d) we deduce the relative cross sections of all three of the above reactions. [Preview Abstract] |
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M6.00005: Scattering length scaling laws for ultracold three-body collisions Jose D'Incao, Brett Esry We have developed a simple and unifying physical picture with which all relevant ultracold three-body collision rates, for short range interatomic interactions, can be derived and understood. The energy and scattering length dependence of the three-body collision rates can be determined from a simple WKB approximation to the tunneling probability through the potential barrier in the initial collision channel. For a given system, the scattering length scaling depends on the number of resonant s-wave interactions as well as on the mass ratio of the particles. Our results are expected to be valid in the threshold regime, i.e., when the collision energy is the smallest energy in the system. (Supported by the National Science Foundation) [Preview Abstract] |
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M6.00006: Analytic expression for three body recombination rates of cold fermionic atoms James Sternberg, J.H. Macek Recombination of fermions in cold three body collisions is investigated using an energy dependent zero range potential (EDZRP) model. Hyperspherical adiabatic potential curves were calculated for several angular momentum states. In the dominant $J^\Pi=1^+$ case for a scattering volume of $V_p = 1 \times 10^{-6} a.u.$ these potential curves are well approximated by an analytic expression. Using this analytic approximation to the hyperspherical adiabatic potential curves and hidden crossing theory we obtain closed form expressions for the three-body recombination rate and recombination cross sections. These expressions depend only on physical parameters such as the scattering length and effective range. \vskip 0.2cm \noindent James Sternberg is supported by the National Science Foundation under grant PHY-997206 [Preview Abstract] |
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M6.00007: LOW TEMPERATURE PLASMAS
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M6.00008: Study of Ultracold Strontium Plasma Priya Gupta, Clayton Simien, Sampad Laha, Ying-Cheng Chen, Thomas Killian Ultracold plasma opens up a new regime in the study of plasma physics. The interest in ultracold plasma stems from the fact that the fundamental processes of thermalization, reionization and recombination in a plasma are very different at the millikelvin temperatures. We laser cool and trap neutral Strontium atoms and then photoionize them to make ultracold plasma. The electron temperature is determined by the photoionizing laser while the ions are at the same temperature as the laser-cooled atoms. At this ultracold temperature, the ions are in the strong coupling regime. Using absorption imaging with 422nm light, we are able to study the various processes in ultracold plasma with excellent spatial, temporal and spectral resolution. This poster will include a description of the apparatus and technique used to create and study ultracold plasma. We will also present results from recent experiments showing plasma oscillations and expansion. [Preview Abstract] |
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M6.00009: External Field Control of Molecular Dynamics Roman Krems, Alexander Dalgarno Inelastic collisions of cold atoms and molecules and dissociation of cold molecules can be manipulated with external electric, magnetic and radiative fields. We show that external field control of molecular dynamics can be based on several principles. Zeeman and Stark effects may remove some of the energetically allowed dissociation paths or they may open closed dissociation channels, leading to suppression or enhancement of the dissociation efficiency. External fields couple the states of different total angular momenta, so that forbidden electronic transitions may become allowed in an external field and the transition rate may be controlled by the field strength. We discuss the range of magnetic fields for magnetic field control of molecular dynamics and outline the prospects for external field control of chemical reactions in binary collisions of cold molecules. [Preview Abstract] |
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M6.00010: Molecular Dynamics Simulations of anti-hydrogen formation in a Penning trap S. X. Hu, D. Vrinceanu, S. F. Mazevet, L. A. Collins Low temperature (4 Kelvin) positrons in a strong magnetic field (5.4 Tesla) of a Penning trap are attached to anti-protons to form anti-hydrogen atoms mainly by three-body recombination. In our simulations 4000 positrons and 1000 anti-protons are confined in a cylindrical geometry. A long time integration (on the order of microseconds) is achieved by using a special adaptive time step symplectic integration scheme. The error in total energy conservation is maintained under 1\% over the entire simulation time interval. Enough recombination events are observed to allow statistical analysis of various quantities. Recombination dependence on initial temperature of antiprotons has also examined. [Preview Abstract] |
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M6.00011: ATOMS IN OPTICAL LATTICES
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M6.00012: Some new results on two-well Bose-Hubbard problem Andrew Carmichael, Marijan Kostrun, Juha Javanainen In continuation of our previous work, we investigate the standard Bose-Hubbard system for a fixed number of particles in a two-well configuration, using the mean-field (semiclassical) approximation and the hermitian phase operator method (quantum). We compare two situations; that in which the on-site interaction is repulsive versus that in which it is attaractive. We find that the respective semi-classical phase spaces are shifted one from the other by an angle $\pi$ and that the spectrum of one system, when inverted, becomes that of the other.We discuss some interesting implications of this duality on the properties of the number fluctuations in the ground state. [Preview Abstract] |
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M6.00013: Optical dipole trap using a Fabry-Perot interferometer as a power buildup cavity Donghyun Cho, Seung Koo Lee, Hyun Sook Lee, Jang Myun Kim We construct an optical dipole trap using a Fabry-Perot interferometer as a power buildup cavity. Large power enhancement allows us to produce 9-mK deep potential wells with $48 \mu$m spot size and 100 nm detuning from the rubidium $D1$ resonance. The optical trap is loaded from a dark- spot MOT which, in turn, is loaded from a low-velocity intense source of ${}^{85}$Rb atoms. Under typical experimental conditions, there are $1.4 \times 10^6$ atoms in 2,000 antinodes of the optical trap. Average atom density is $1.1 \times 10^{12}$ ${\rm cm^{-3}}$. The number of trapped atoms is limited by the atom density, or trapping volume. The standing wave configuration with tight longitudinal confinement has much smaller trapping volume compared with the equivalent travelling wave. A method to convert the trap to a travelling- wave like configuration using phase modulation is studied. In addition, we studied possibilities of tuning the resonance frequency of the Fabry-Perot resonator by using trapped atoms. [Preview Abstract] |
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M6.00014: Cold Atomic Strontium: Precision Spectroscopy and Optical Frequency Standards Tanya Zelevinsky, Tetsuya Ido, Martin Boyd, Andrew Ludlow, Sebastian Blatt, Jun Ye Progress toward the neutral strontium frequency standard has been made on several fronts. Robust narrow line cooling on the 689 nm 1S0 - 3P1 transition of bosonic strontium-88 was demonstrated and studied in detail, and precision spectroscopy of strontium atoms at 1 uK was performed in free space. The laser systems needed to realize cooling and trapping of fermionic strontium-87 for developing an optical standard based on a 1 mHz-wide 1S0 - 3P0 transition have been installed, and ultracold atoms have been loaded into a one-dimensional optical lattice operating at a wavelength where the ac Stark shifts of the ground and excited states of the clock transition are equal. A highly stabilized and compact 698 nm laser source was built to serve as the local oscillator for the atomic clock, and preliminary spectroscopic results in the lattice are presented. In addition, work is in progress on a recently proposed EIT clock scheme that operates on the forbidden strontium-88 1S0 - 3P0 transition. [Preview Abstract] |
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M6.00015: Superfluid-insulator transition in a moving system of interacting bosons Anatoli Polkovnikov, Ehud Altman, Eugene Demler, Bert Halperin, Mikhail Lukin We analyze stability of superfluid currents in a system of strongly interacting ultra-cold atoms in an optical lattice. We show that such a system undergoes a dynamic, irreversible phase transition at a critical phase gradient that depends on the interaction strength between atoms. At commensurate filling, the phase boundary continuously interpolates between the classical modulation instability of a weakly interacting condensate and the equilibrium quantum phase transition into a Mott insulator state at which the critical current vanishes. We argue that quantum fluctuations smear the transition boundary in low dimensional systems. Finally we discuss the implications to realistic experiments. [Preview Abstract] |
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M6.00016: Characterization of a far-off resonant optical lattice trap for quantum entanglement of neutral atoms Raymond Newell, Jinwei Wu, Xinxin Zhao, David Vieira Far-off resonant optical lattice (FORL) traps offer several advantages for manipulating neutral atoms toward quantum entanglement. Low photon scattering rates can lead to long coherence times, properly chosen lattice constants permit single-site resolution and addressing, and atoms may be transported by altering the phase or geometry of intersecting lattices. We describe our efforts to combine all these advantages in a CO-2 laser standing-wave lattice trap. After loading Rb-87 atoms from a standard magneto-optical trap (MOT) into our CO-2 lattice, we will adiabatically transfer them into a lattice of smaller lattice constant (0.5 microns) which will allow a spin-spin entanglement rate near 0.2 Hz. Adiabatically transferring the atoms back into the CO-2 lattice will permit readout of the atomic state and study of the entanglement effects. Our progress toward optical resolution of the 5.3 micron lattice sites is discussed, and characterization of the FORL potential by parametric excitation is presented. [Preview Abstract] |
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M6.00017: Neutral atom quantum computing architecture based on 1D and 2D optical lattices on a chip Katharina Christandl, Rajani Ayachitula, Michael Chmutov, Gregory P. Lafyatis, Seung-Cheol Lee, Jin-Fa Lee We present results of our investigation of neutral atom quantum computing architectures using 1D and 2D optical lattices on a chip. Previously, we have shown that lattices can be created above an optical waveguide by destructively interfering different, co-propagating waveguide modes of blue-detuned laser light [1]. The optical lattice nodes are suitable for tightly trapping single atoms, which can in turn serve as individually addressable qubits in a quantum memory. We are studying details of these systems including the polarization of the light around optical lattice nodes and the resulting Zeeman substate-dependence of the trapped-atom dynamics. We also explore the possibilities of moving traps within a lattice, entangling pairs of trapped atoms, and, ultimately, realizing one- and two-qubit gates. 1. Phys. Rev. A 70 032302 (2004). [Preview Abstract] |
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M6.00018: DEGENERATE FERMI GASES
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M6.00019: Crossover from fermionic to bosonic quantum gases Jochen Wachter, John Cooper, Murray Holland Correlations between a composite boson and a fermion pair are considered in the context of the crossover theory of fermionic to bosonic superfluidity. It is shown that such correlations are the minimal ingredients needed in a many-body theory to generate the right boson-boson scattering length in the Bose-Einstein limit of the crossover. This is applied to the formation of molecules in the normal phase which can be compared with experimental data in the available alkali systems. [Preview Abstract] |
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M6.00020: Optical Molecular Spectroscopy of the BEC/BCS Crossover in $^{6}$Li R. I. Kamar, G. B. Partridge, K. E. Strecker, M. W. Jack, R. G. Hulet The many-body state of fermionic $^{6}$Li near a Feshbach resonance is probed using optical molecular spectroscopy. We evaporatively cool a degenerate spin mixture of fermionic $^{6} $Li in an optical trap to form a condensate of dressed molecules at 754 G. The condensate is detected by absorption imaging. The dressed molecules are a superposition of singlet molecules and triplet free atoms. A laser is used to project the dressed molecules onto an excited molecular state, in order to measure the singlet component. The bare singlet molecule fraction is determined by measuring the resulting loss of atoms. Our results show that the molecular contribution to the dressed molecule superposition is orders of magnitude larger than predicted by two-body physics. We have also observed coherent oscillations between atoms and molecules induced by the optical probe when tuned to the bare molecular resonance. [Preview Abstract] |
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M6.00021: Spectroscopic Evaluation of Degeneracy in Dilute Weakly Interacting Degenerate Fermi Gases Marijan Kostrun, Robin Cote We consider an application of two-photon Raman probe spectroscopy to detect the onset of degeneracy in a sample of ultra-cold atomic fermions that underwent Bardeen-Cooper-Schiefer instability. We show how the method allows us to obtain lineshapes that reveal a signature of Cooper pairs: the location and width of the superfluid gap. We discuss the applicability of the method in realistic conditions for $^6$Li prepared in two different hyperfine states. [Preview Abstract] |
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M6.00022: Investigating the BCS-BEC crossover region using ultra-cold fermionic atoms John Stewart, Markus Greiner, Cindy Regal, Deborah Jin Recently, ultra-cold atom experiments have allowed researchers access to the BCS-BEC crossover. Starting with a two-component gas of $^{40}$K atoms cooled to quantum degeneracy, a magnetic field Feshbach resonance is used to create strong, tunable interactions in the gas. We report on recent experiments including the observation of pair-correlated atoms through the atom shot-noise in time-of-flight absorption images. [Preview Abstract] |
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M6.00023: Quasiparticles and order parameter near quantum phase transition Miron Amusia, Alfred Msezane, Vasily Shaginyan We have shown that the Landau paradigm based upon both the quasiparticle concept and the notion of the order parameter is valid and can be used to explain the anomalous behavior of the heavy fermion metals near quantum critical points. The understanding of this phenomenon has been problematic largely because of the absence of theoretical guidance. Exploiting this paradigm and the fermion condensation quantum phase transition, we investigate the anomalous behavior of the heavy electron liquid near its critical point at different temperatures and applied magnetic fields. We show that this anomalous behavior is universal and can be used to capture the essential aspects of recent experiments on the heavy-fermion metals at low temperatures. In contrast with the conventional Landau quasiparticles, the effective mass of the quasiparticles in question strongly depends on the temperature and the applied magnetic field, while the order parameter is destroyed at any finite temperature. We have demonstrated that this unusual behavior of both the order parameter and the quasiparticles is determined by the fermion condensation quantum phase transition which allows the existence of the quasiparticles down to the lowest temperatures. In that case we obtain a unique possibility to control the essence of the HF metals by magnetic fields in a wide range of temperatures. [Preview Abstract] |
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M6.00024: Strongly Interacting Spin-Polarized Fermions in Quasi-1D Traps: Interactions and Correlations Scott Bender, Kevin Erker, Brian Granger When confined to quasi-one-dimensional (1D) geometries, spin-polarized fermions can have strong effective 1D interactions. This opens up the possibility of studying a fermionic version of the Tonks-Girardeau gas of impenetrable bosons. In the fermionic Tonks-Girardeau gas, strongly interacting 1D fermions are dual to weakly interacting 1D bosons. We describe both the two particle scattering physics leading to these strong effective 1D interactions and the correlations that these interactions create in the many body system. We will also discuss the prospects for studying this system in ultracold atom gases. [Preview Abstract] |
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M6.00025: Stability of fermionic Feshbach molecules in a Bose-Fermi mixture Alexandr Avdeenkov, Daniele Bortolotti, John Bohn In the wake of successful experiments in Fermi condensates, experimental attention is broadening to include to resonant interactions in degenerate Bose-Fermi mixtures. We consider the properties and stability of the fermionic molecules that can be created in such a mixture near a Feshbach resonance (FR). To do this, we consider the two-body scattering problem in the many-body environment, and assess its complex poles. The stability properties of the resulting molecules strongly depend on the center-of-mass motion of a molecule, which has to be taken into account because of its fermionic nature. At low center-of-mass momenta the molecules are more stable than in the absence of the environment (due to Pauli-blocking effects), while at high center-of-mass momenta the molecules are less stable. [Preview Abstract] |
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M6.00026: Bose-Fermi Mixtures Near an Interspecies Feshbach Resonance: A Non Equilibrium Analysis Daniele Bortolotti, Alexandr Avdeenkov, John Bohn We study the non equilibrium behavior of a Bose-Fermi mixture of alkali atoms in the presence of a Feshbach resonance between bosons and fermions. To this end we derive the Hartree-Fock-Bogoliubov (HFB) equations of motion for the interacting system. This approach has proven very successful in the study of resonant systems composed of either Bose or Fermi particles. Inspection of these equations and numerical solution show that this approach is not adequate for a thorough analysis of the system at hand, and that even the simple physics of the system is driven by higher order correlations between components. [Preview Abstract] |
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M6.00027: LASER COOLING AND TRAPPING II
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M6.00028: An Optical Dipole Trap for 87-Rubidium Justin Brown, Dwight Whitaker Using a high numerical aperture optical system, we have loaded $^ {87}$Rb atoms into an optical dipole trap created by a 100 W CO$_2$ laser. The design of our system allows us to load our trap under a wide range of conditions. We will discuss key parameters to maximize the transfer of atoms from our MOT cloud to the dipole trap in preparation for evaporative cooling en route to BEC. In addition, we present thoughts on techniques to further increase the number of atoms in the dipole trap. [Preview Abstract] |
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M6.00029: Parametric Excitation in a Magneto-optical Trap with Modulating the Magnetic Field Gradient Yonghee Kim, Dahyun Yum, Chang-Il Ryoo, Kihwan Kim, Wonho Jhe, Heung-Ryoul Noh Parametric resonance is a very interesting and important mechanism in divergent systems from physics to biology. Recently, there were a lot of researches relating to the parametric excitation in the magneto-optical trap system. However, the previous investigations were executed by only modulating the cooling laser intensity. While the intensity modulation showed the limit cycle motion and Hopf-bifurcation, the magnetic field gradient modulation revealed the more interesting phenomena such as period doubling, chaos, and so on. We have studied the transition problems between two attractors in period doubling area which are much far from equilibrium and could not be understood by the method used in limit cycle motion. The magnetic field modulation methods could give quantitative comprehensions of transition problems in the non-equilibrium system that has not been studied. [Preview Abstract] |
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M6.00030: Cooling of Atoms Using an Asymmetric One-Way Barrier Artem Dudarev, Michael Marder, Qian Niu, Nathaniel Fisch, Mark Raizen We show how to construct asymmetric optical barriers for atoms. These barriers can be used to compress phase space of a sample by creating a confined region in space where atoms can accumulate with heating at the single photon recoil level. We describe how the wall can be created with a simple two-level model and then show how it can be applied to more realistic multi-level atoms. The phase space compression is illustrated in two regimes: (i) when the wall is placed in the middle of a box potential and atoms are collected in the smaller region; (ii) when it is moved in the concave potential with a finite velocity. In both cases we derive analytical expression for compression and compare them with numerical simulations of collisonless gas. [Preview Abstract] |
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M6.00031: Laser Spectroscopic Determination of the Nuclear Charge Radius of $^6$He and $^8$He P. Mueller, L.-B. Wang, K. Bailey, J.P. Greene, D. Henderson, R.J. Holt, R.V.F. Janssens, C.L. Jiang, Z.-T. Lu, T.P. O'Connor, R.C. Pardo, K.E. Rehm, J.P. Schiffer, X.D. Tang, G.W.F. Drake Laser spectroscopic measurements of atomic isotope shifts provide unique access to the nuclear charge distribution of short-lived isotopes. The isotopes of interest for this study are $^6$He (t$_{1/2}$ = 807 ms) and $^8$He (t$_{1/2}$ = 119 ms), which exhibit a loosely bound neutron halo around an $\alpha$-like core. Charge radii measurements of both isotopes provide corroboration for their halo structure and test nuclear structure theories of light nuclei. We have performed high-resolution laser spectroscopy on individual $^6$He atoms captured in a magneto-optical trap. This technique enabled us to accurately measure the atomic isotope shift between $^6$He and $^4$He in the $2^3S_1 \rightarrow 3^3P_2$ transition. Based on this result and precision atomic theory calculation of this two electron system, the root-mean-square charge radius of the $^6$He nucleus could be determined to be 2.054(14)fm [1]. Currently, we are working to expand this technique to also measure $^8$He and we will report on first results from a $^8$He production experiment at the ATLAS facility at Argonne. [1] L.-B. Wang {\it et al.}, PRL 93, 142501 (2004).\\ {\it This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. W-31-109-ENG-38.} [Preview Abstract] |
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M6.00032: Effects of Degeneracy and Excited-State Spectral Overlap on Sub-Doppler Laser Cooling Josh W. Dunn, Chris H. Greene Using the Monte Carlo wave-function technique, we perform fully quantum calculations of 3D laser cooling for atoms with nonzero nuclear spin. The calculations lead to predictions for the temperature of atoms cooled in both the $\sigma_{+}$-$\sigma_{-}$ and the lin $\perp$ lin laser configurations. We explore the effect of increased cooling due to internal atomic degeneracy and decreased cooling due to spectral overlap of hyperfine excited states. The results of these competing effects are revealed for various fermionic alkaline-earth atoms and fermionic Yb. [Preview Abstract] |
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M6.00033: Towards quantum degeneracy in ultracold neutral strontium S.B. Nagel, A.D. Saenz, Y.N. Martinez, P.G. Mickelson, Y.C. Chen, T.C. Killian We report continued studies of ultracold neutral Strontium in a magneto-optical trap operating on the $^{1}$S$_{0}${\_} $^{3}$P$_{1}$ intercombination line at 689 nm. Our recent determination of the $^{1}$P$_{1}$ atomic lifetime via photoassociative spectroscopy at extremely large internuclear separation has motivated the construction of an apparatus including a new dipole trap. Adding a dipole trap will allow us to achieve higher densities in the pursuit of quantum degeneracy in Strontium. [Preview Abstract] |
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M6.00034: Continuous Propagation of Magnetically Guided Dark State $^{87}$Rb Spencer Olson, Rahul Mhaskar, Georg Raithel We demonstrate the coupling of a continuous, cold atomic beam into a 1.8~m long high-gradient (2.4~kGauss/cm) magnetic guide. Atoms are extracted from an LVIS-MOT and injected into the guide using a continuously operating moving optical molasses. By combining field geometries of our guide with that of a moving optical molasses, we estimate reaching coupling efficiencies $>$50\%. Before injection, the atoms are transferred into a dark state, eliminating trap losses due to resonant scattering of stray MOT light. The injection mechanism will be described in detail. After gravitational slowing and magnetic compression, the atomic beam has an average velocity of 50~cm/s. Measurements of the transverse and longitudinal temperatures will be presented. We have found temperature values of 150$\pm$30~$\mu$K and 950~$\mu$K, respectively; the value on the longitudinal temperature represents an upper limit. Further applications, such as continuous evaporative cooling of the beam and cw BEC will be discussed. [Preview Abstract] |
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M6.00035: WAVEPACKET DYNAMICS AND COHERENT CONTROL
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M6.00036: Sudden switching in qubits Khazhgery Shakov, Jim McGuire, Lev Kaplan, Dmitry Uskov, Athanasios Chalastaras We present an analytic description of the dynamics of a two-state system strongly perturbed by a series of rapidly changing pulses (`kicks'). The evolution matrix for a series of kicks is expressed as a time ordered product of single pulse matrices. The effects of time ordering for different sequences of pulses are analyzed. The detailed results are given for a single pulse and combinations of two or three pulses. Generalization into an arbitrary number of pulses is also discussed. The effects of a finite width of the pulses are studied numerically. [Preview Abstract] |
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M6.00037: Applying Principle Control Analysis to Optical Pulse Shapes Optimized for Selective Fragmentation of Clusters K. J. Betsch, E. Wells Principal control analysis has been applied to the results of a learning algorithm search that optimized optical pulse shapes for selective fragmentation of $S_8$ clusters. This technique reduces the control dimensions needed for pulse shape optimization for this multiphoton process. Pulse shapes optimized for ionization/fragmentation generally require more control directions than the stimulated Raman scattering processes explored by White {\it et al}\thanks{J. L. White, B. J. Pearson, and P. H. Bucksbaum, J. Phys. B {\bf 37}, L399 (2004).}$^2$. Thus, despite using principal control analysis, it still appears difficult to extract information about the quantum dynamics of higher order processes from the optimized pulse shape. %[1] J. L. White, B. J. Pearson, and P. H. Bucksbaum, J. Phys. B %{\bf 37}, L399 (2004). [Preview Abstract] |
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M6.00038: Atomic Fountain Measurements of Multiple Quantum Transitions in Cesium Jason Amini, Harvey Gould, Charles Munger An atomic fountain is used to study transitions between the $m_F$ sublevels of the Cs $F=4$ $6S_{1/2}$ ground state in magnetic and electric fields. Flop-in and flop-out transitions are induced by coils surrounding the interaction region with which we can apply rf pulses of arbitrary duration, amplitude, shape, phase, and direction. Results from some of these studies will be presented. [Preview Abstract] |
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M6.00039: Interpreting Closed-Loop Learning Control of MolecularFragmentation in Members of the Ketone Family of Molecules Mark Baertschy, David Cardoza, Thomas Weinacht We present the results of closed-loop learning control over molecular fragmentation in the ketone family, CH$_n$X$_m$COCY$_3 $, with X being Br or H; Y being H, D, F or Cl; and with n + m = 3. The experiments used shaped ultrafast laser pulses and a Genetic Algorithm controlling a pulse shaper. Pump-probe measurements were also carried out to supplement the learning control results. To interpret our learning control and pump-probe results, we used a combination of \textit{ab initio} molecular structure calculations, modifications to the learning algorithm, and quasi-static molecular ionization calculations. For CH$_3$COCF$_3$ we discovered that the control mechanism is based on a subtle interplay between ionization enhancement and the details of the dissociation dynamics. We have since generalized these ideas to gain insight into the fragmentation control mechanisms for a broad class of molecules. [Preview Abstract] |
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M6.00040: Effect of Pulse Asymmetry on Strongly Driven Two-Level Systems C.W.S. Conover, R.O. Wilson We present an experimental study of the interaction between an effective two-level system and strong radiation pulses as a function of symmetry and energy of the pulse. We have explored the behavior of the transition probability as a function of pulse area and the degree of asymmetry for Gaussian, Lorentzian and hyperbolic secant pulses. The experimental system consists of fine-structure levels of Rydberg states in alkali atoms. Raman transitions are driven through far-off-resonance intermediate states. The pulses are in the microwave regime and have high fidelity, $F \ge 0.995$, and uniform intensity. Experiments were performed with pulses that range from nearly diabatic evolution to nearly adiabatic evolution. It is shown that for highly asymmetric pulses that the population transfer is independent of pulse area. [Preview Abstract] |
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M6.00041: CAVITY QED
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M6.00042: Generating entangled photon pairs from a cavity QED system Bo Sun, Duanlu Zhou, Li You We propose a scheme for the controlled generation of Einstein-Podosky-Rosen (EPR) entangled photon pairs from an atom coupled to a high-Q optical cavity, extending the prototype system\footnote{C. K. Law and H. J. Kimble, J. Mod. Opt. \textbf{44}, 2067 (1997)} as a source for deterministic single photons. A thorough theoretical analysis confirms the promising operating conditions of our scheme as afforded by currently available experimental setups. Our result demonstrates cavity QED system as an efficient and effective source for generating entangled photon pairs, and shines new light on its important role in quantum information science. [Preview Abstract] |
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M6.00043: Progress Towards a Cavity QED system for Quantum Infomration K.M. Fortier, S. Kim, M. Gibbons, M.S. Chang, Michael Chapman Ultracold $^{87}$Rb atoms are delivered into a high-finesse optical micro-cavity using a translating optical lattice trap and detected via the cavity field. Our cavity satisfies the strong-coupling requirements for a single intracavity atom, thus permitting real-time observation of single atoms transported into the cavity. Recent improvements to trap transport, trap lifetime, and active cavity locking lead towards a workable cavity QED experiment for quantum information. [Preview Abstract] |
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M6.00044: Cavity QED and Atom Chips Thomas Purdy, Subhadeep Gupta, Kevin Moore, Kater Murch, Dan Stamper-Kurn We report our recent progress toward combining the technologies of microfabricated magnetic atom traps and high finesse optical cavities. We are pursuing a design in which one small lithographically patterned mirror is surrounded by current- carrying wires which allow for the controlled delivery of cold atoms into the cavity. The other half of the cavity is formed by a macroscopic mirror suspended above the chip. Details of the fabrication and component testing are discussed. [Preview Abstract] |
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M6.00045: Cavity quantum electrodynamics with surface plasmons Darrick Chang, Anders Sorensen, Mikhail Lukin The possibility of implementing cavity QED on a solid-state microchip has been explored recently [childress04,sorensen04,blais04,wallraff04]. These ideas involve strong coupling between microwave emitters and superconducting transmission lines. It is desirable to extend these ideas into the optical domain because of smaller mode volumes and faster operations, and because optical photons are ideal for long-range quantum communication. Here we propose a novel approach to accomplish this, based on strong coupling between optical emitters and electromagnetic surface modes, or surface plasmons, confined to a sub-wavelength nanowire. The tight transverse confinement of the plasmons on a scale of the wire radius $R$ enables strong coupling between plasmons and nearby emitters. We explore the possibility of efficient single photon generation and long-range coupling of quantum bits in such a system. \newline \newline [childress04] L. Childress, A.S. S{\o}rensen, and M.D. Lukin, Phys. Rev. A \textbf{69}, 042302 (2004). \newline [sorensen04] A.S. S{\o}rensen \textit{et al.}, Phys. Rev. Lett. \textbf{92}, 063601 (2004). \newline [blais04] A. Blais \textit{et al.}, Phys. Rev. A \textbf{69}, 062320 (2004). \newline [wallraff04] A. Wallraff \textit{et al.}, Nature \textbf{431}, 162 (2004). [Preview Abstract] |
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M6.00046: POSITRON SCATTERING
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M6.00047: Ortho- and Para-Positronium Formation Measurements for Positron Scattering by C$_2$H$_2$ and CH$_4^\ast$ J. Edwards, D. Duong, W. E. Kauppila, E. G. Miller, T. S. Stein, E. Surdutovich We are investigating ortho- and para-positronium formation for positrons interacting with C$_2$H$_2$ and CH$_4$ in a gas scattering cell. These measurements involve the detection of two $\gamma$ rays in coincidence for energy windows (1) centered at 511~keV resulting from the decay of short-lived (0.1~ns) para-Ps and the destruction of longer-lived (0.1~ms) ortho-Ps at the scattering cell walls, and (2) from 300 to 460~keV resulting from the three gamma decay of ortho-Ps.$^1$ By taking the ratios of these signals versus positron impact energy we find that near the Ps formation threshold the $3\gamma/2\gamma$ ratios have their largest values of about 1.6, which is where Ps has its lowest kinetic energy and ortho-Ps decays without breakup at the cell walls. Comparing these ratios with ones obtained for Ar$^1$ reveal interesting differences, which include the formation of Ps with inner orbital electrons. The threshold we observe for forming Ps with CH$_4$ is consistent with this being an adiabatic ionization process, as opposed to a vertical ionization process.\\ $^\ast$Research supported by NSF Grant PHY 99-88093.\\ $^1$W.E. Kauppila et al. Phys. Rev. Lett. 93, 113401 (2004). [Preview Abstract] |
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M6.00048: Ortho- and Para-Positronium Formation Measurements for Positron Scattering by N$_2$ and CO$^\ast$ Erik Miller, Dao Duong, Jessica Edwards, Walter Kauppila, Talbert Stein, Eugene Surdutovich We are investigating ortho- and para-positronium formation for positrons interacting with N$_2$ and CO in a gas scattering cell. These measurements involve the detection of two gamma rays in coincidence for energy windows (1) centered at 511~keV resulting from the decay of short-lived (0.1~ns) para-Ps and the destruction of longer-lived (0.1~ms) ortho-Ps at the scattering cell walls, and (2) from 300 to 460 keV resulting from the three gamma decay of ortho-Ps.$^1$ By comparing our $3\gamma/2\gamma$ ratios to those for other target gases$^1$ we find a strikingly anomalous behavior at the Ps formation threshold for N$_2$ where there is an unexpected enhancement of the $2\gamma $ signal compared to the $3\gamma$ signal, while for CO (isoelectronic with N$2_$) the behavior is consistent with the other gases. The anomalous behavior for N$_2$ is consistent with an enhancement of annihilation at the threshold, which is as if Ps is forming and remaining bound to the N$_2^+$ ion until annihilation occurs.\\ $^\ast$Research supported by NSF Grant PHY 99-88093.\\ $^1$W.E. Kauppila et al. Phys. Rev. Lett. 93, 113401 (2004). [Preview Abstract] |
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M6.00049: Cross-section for formation of the triplet positron-helium bound state Joseph Di Rienzi, Richard Drachman The state consisting of a positron bound to the first triplet excited state of helium was conjectured to exist long ago [1] and established rigorously recently [2]. In Ref. [1] it was suggested that an efficient way to form this interesting system would be by collision of positronium and ground-state helium: Ps+He[$^{1}$S]$\to $He($^{3}$S$^{e})$e$^{+}$+e$^{-}$. The idea is that a target of natural helium would be convenient, although the positronium beam is technically difficult. In addition, the cross-section should be of atomic size. Competing with this process would be radiative capture of a positron on metastable triplet helium. We are working to evaluate cross-sections for both these processes, using the Born approximation and simplified initial and final wave functions. [1] R. J. Drachman, Y. K. Ho, and S. K. Houston, J. Phys. B \textbf{9}, L199 (1976) [2] G. G. Ryzhikh and J. Mitroy, J. Phys. B \textbf{31}, 3465 (1998). [Preview Abstract] |
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M6.00050: Positron Impact Ionization in Noble Gas Atoms and Diatomic Molecules J.P. Marler, C. M. Surko Results are presented for absolute positronium formation and direct ionization by positron impact on Ne, Ar, Kr, Xe, N$_2$, CO and O$_2$ at energies from threshold up to 90~eV. The experiments use a high-resolution, trap-based positron beam and exploit the properties of positron orbits in a magnetic field [1]. Results for the noble gases are compared with theoretical predictions and with measurements obtained using a significantly different method [2]. Results for diatomic molecules are compared to other available measurements and theoretical calculations where available. There is generally good agreement between the experimental measurements, providing an important benchmark for theoretical calculations. Intriguing features in Ar and O$_2$ will be discussed.\\ ~[1] J.P. Sullivan, S.J. Gilbert, J.P. Marler, R.G. Greaves, S.J. Buckman and C.M. Surko., \textit{Phys. Rev. A.} \textbf {66}, 042708 (2002)\\ ~[2] J.P. Marler, J.P. Sullivan and C.M. Surko, \textit{Phys. Rev. A} (2005), in press. [Preview Abstract] |
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M6.00051: New results for positron-molecule Feshbach resonances and bound states. J.A. Young, L.D. Barnes, C.M. Surko Monoenergetic positrons from a trap-based beam have been used to measure the first energy resolved positron-on-molecule annihilation spectra [1,2]. Strong peaks in annihilation rate are observed at energies just below the vibrational modes of various molecules. These peaks are due to vibrational Feshbach resonances (VFR) and provide evidence of positron- molecule binding. In this paper, the properties of these VFR are further explored. The dependence on target morphology is studied for the ring hydrocarbons, benzene, cyclohexane and cyclopropane. A comparison is presented of positron-annihilation and infrared-absorption spectra. Finally, evidence is presented for a second, ``positronically excited'' bound state in large alkane molecules.\\ ~[1] S. J. Gilbert, \textit{et al.}, \textit{Phys. Rev. Lett}., \textbf{88}, 043201 (2002).\\ ~[2] L. D. Barnes, \textit{et al.}, \textit{Phys. Rev. A} \textbf {67}, 032706 (2003). [Preview Abstract] |
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M6.00052: Hyperspherical hidden crossing calculation of Ps formation cross section for low-energy $\mbox{e}^+-\mbox{Li}$ collisions Janine Shertzer, Sandra Ward Using the hyperspherical hidden crossing method (HHCM), we have computed the $s$-, $p$-, $d$- and $f$-wave Ps formation cross sections for $\mbox{e}^+-\mbox{Li}$ collisions in the energy range $0-1.8$eV.\footnote{ S.J. Ward and J. Shertzer, Phys. Rev. A \textbf{68}, 032720 (2003).}$^,$\footnote{ S.J. Ward and J. Shertzer, Nucl. Instr. and Meth. in Phys. Res. B \textbf{221}, 206 (2004).} We have also computed the partial wave cross sections by including a correction term to the HHCM that arises from the one-Sturmian theory ($\mbox{HHCM}^{+\mbox{cor}})$. The effect of including the core polarization term in the model potential was also investigated (HHCM$_{\mbox{cp,}} $ HHCM$_{\mbox{cp}}^{+\mbox{cor}} $ ). The Stuckelberg phase varied only slightly with the incident positron momentum and decreased in a systematic way with increasing partial wave $L.$ The $f$-wave contribution to the Ps formation cross section was significant near the Li(2$p)$ threshold. In all four calculations the cross section summed over the lowest four partial waves lies between the experimental measurements of the lower and upper limits.\footnote{ E. Surdutovich, J.M. Johnson, W.E. Kauppila, C.W. Kwan and T.S. Stein, Phys. Rev. A \textbf{65}, 032713 (2002); private communication.\par } [Preview Abstract] |
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M6.00053: High-lying resonances in positron scattering by the helium ion below the Ps($n$=3) threshold Z.-C. Yan, Y.K. Ho Ever since Bhatia and Drachman [1] reported two $S$-wave resonances in positron scattering by a helium ion, there has been considerable interest in and sometimes controversial on the investigation of the resonances in such a system [2]. In the present work, we apply the method of complex-coordinate rotation to investigate resonances in positron scattering by helium ions. Highly correlated Hylleraas functions are used to calculate resonances for high-angular-momentum states up to $L=9$. We will report the results for high-lying resonances below Ps($n$=3) threshold. A comparison will be made with the available results in the literature. \\ \ \\ \noindent [1] A. K. Bhatia and R. J. Drachman, Phys. Rev. A {\bf 42}, 5117 (1990) \\ \noindent [2] Y. K. Ho, Phys. Rev. A {\bf 53}, 3165 (1996); A. Igarashi and I. Shimamura, Phys. Rev. A {\bf 56}, 4733 (1997); Y. K. Ho and Z.-C. Yan, Phys. Rev. A {\bf 66}, 062705 (2002); A. Igarashi and I. Shimamura, Phys. Rev. A {\bf 70}, 012706 (2004); N. Yamanaka, et al. Phys. Rev. A {\bf 70}, 062701 (2004) [Preview Abstract] |
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M6.00054: ELECTRON SCATTERING II
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M6.00055: Dissociative recombination study of HCO$^+$ Stefano Tonzani, Aasa Larson, Robin Santra, Chris H. Greene From accurate quantum chemistry calculations, we have found that the electron collision dynamics of HCO$^+$ is driven by capture into Rydberg states. The Renner-Teller effect is not important for higher Rydberg states. From calculated potentials, the effective quantum numbers are fitted in three dimensions. The full vibrational dynamics of the molecule is considered, and the joint electron-nuclear dynamics is treated using quantum defect theory and a frame transformation approach. Results on autoionization widths for Rydberg states and dissociative recombination cross section are given. [Preview Abstract] |
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M6.00056: Theoretical study of dissociative recombination of tri-atomic molecular ions Viatcheslav Kokoouline, Chris H. Greene We consider the process of dissociative recombination of tri-atomic ions. Successful theoretical treatment of the dissociative recombination in H$_3^+$ motivated us to extend the treatment to other small molecular ions. The most straightforward extension is to apply the treatment to other isotopomers of H$_3^+$. In this work, we calculated the dissociative recombination rate of H$_2$D$^+$ and D$_2$H$^+$. To represent properly vibrational motion we use hyperspherical coordinates within so-called Slow Variable Representation. The calculated rates for the dissociative recombination of H$_2$D$^+$ and D$_2$H$^+$ are in good agreement with recent experiments in storage rings. In this work, we also suggest a possible solution to the problem posed by a recent stationary afterglow experiment. In that experiment, a very low dissociative recombination rate was found that seems to contradict with the results from storage ring and our calculation. In addition, preliminary results for the dissociative recombination in HCO$^+$ are presented. This work is supported by NSF-ITR grant #PHY-0427460 [Preview Abstract] |
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M6.00057: State-Selective Single-Electron Capture by Ne$^{q+}$ (q = 3 -- 6) Ions from H$_{2}$ O and CO$_{2}$ O. Abu-Haija, R. Sacks, S. M. Ferguson, E. Y. Kamber Using translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of Ne$^{q+}$ recoil ions with H$_{2}$O and CO$_{2}$ at laboratory impact energies between 15 and 200 qeV (q = 3 - 6, where q is the projectile charge state) and scattering angles between 0\r{ } and 5\r{ }. The translational energy-gain spectra show that only a few final states were selectively populated depending on the charge state of the projectile. In all collision systems studied here, the dominant reaction channels are due to non-dissociative single-electron capture into excited states of the projectile product. The final state populations will be discussed on the basis of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. Additional measurements of differential cross sections compared with available theoretical calculations will also be presented. [Preview Abstract] |
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M6.00058: Low Energy Electron Capture by Multi-Charged Ions using Merged Beams C.C. Havener, R. Rejoub Low energy electron capture cross sections are measured at the ORNL Multi-charged Ion Research Facility (MIRF) using the ion- atom merged-beams technique. Absolute measurements are performed for multi-charged ions with H(D) and Li from keV/u to meV/u. The ion-atom merged-beams apparatus is being upgraded to take advantage of the higher velocity and higher quality beams produced by the ORNL High Voltage platform. Details of the design and expected first measurements will be presented. Improvements include access to lower energies with better energy resolution for measurements with both H and D. Electron capture measurements with heavy atomic and molecular ions below an eV/u are now possible. [Preview Abstract] |
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M6.00059: \textit{Ab initio} Study of Dissociative Electron Attachment to ClCN and BrCN J. Royal, A. E. Orel ClCN and BrCN are pseudobihalogens, that is both CN and Cl/Br have positive electron affinities. This means that dissociative electron attachment is possible into two final fragment channels, CN$^{-}$ and Cl$^{-}$/Br$^{-}$. The resonance parameters for this system are obtained from electron scattering calculations using the Complex Kohn Variational method. These resonance parameters are used as input into both a time-dependent wave packet calculation and a time-independent calculation using the discrete variable representation and exterior complex scaling . The calculated cross sections will be reported and compared to available experiment. Work supported by the NSF PHY-02-44911 and from The Center for Biophotonics, an NSF Science and Technology Center PHY 0120999. [Preview Abstract] |
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M6.00060: Radiative Recombination in ultracold plasmas Gouthaman Balaraman, Raymond Flannery A symmetrized version of the Heisenberg correspondence principle is proposed and is used to derive ``classical" radial matrix elements for continuum-bound transitions. Classical cross sections for radiative recombination at low energies into a particular $n,\ell$ state are then derived and shown to be in excellent agreement with the quantal results. Classical cross sections also provide excellent agreement with the Kramers formula. Semi-classical transition probabilities for radiative cascade out of low $l$ Rydberg states have been derived. Results for radiative recombination into and radiative transitions out of various $n, \ell states$ are illustrated. [Preview Abstract] |
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M6.00061: Determination of an $(e,2e)$ apparatus instrument function using a SIMION simulation B.A. deHarak, N.L.S. Martin The motivation for this work were recent $(e,2e)$ experiments on the angular distribution of electrons, {\em scattered} through a range of angles, in coincidence with electrons {\em ejected} at $\pm90^\circ$ with respect to a 488eV incident electron beam. In general there was excellent agreement between the experimental data and distorted wave Born approximation calculations (see poster by deHarak {\it et al.}, this conference). However there were apparent discrepancies at small scattering angles and it was unclear whether this was a real effect or was due to the finite (unknown) angular acceptance of our electron spectrometer. We have therefore begun an extensive effort to model the apparatus using SIMION 3D 7.0 Ion and Electron Optics Software. The results presented will include the effect due to the finite volume of the interaction region, as well as the electron lens plus hemispherical analyzer system. [Preview Abstract] |
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M6.00062: Momentum transfer dependence of the He $(e,2e)$ cross section: scattered electron angular distributions B.A. deHarak, N.L.S. Martin, Zhangjin Chen, D.H. Madison In recent work we measured the angular distribution of electrons, {\em scattered} through a range of angles $-30^\circ$ to $+30^\circ$, in coincidence with electrons {\em ejected} at $\pm90^\circ$ with respect to a 488eV incident electron beam. We presented the data as the {\it sum} and {\it difference} of scattered electron angular distributions. There was excellent agreement between the experiments and distorted wave Born approximation calculations -- provided that post collision interaction effects were included.\footnote{B.A. deHarak, Zhangjin Chen, D.H. Madison, and N.L.S. Martin, submitted to J.Phys.B} The calculations predicted an interesting zigzag feature in the {\it difference} angular distribution at small angle scattering, but there were not enough data points at small angles to test this prediction. We have now carried out more extensive measurements in this angular region and will present our results. We will also present measurements and calculations for ejected electron directions $+75^\circ$ and $-105^\circ$; the results demonstrate that the $(e,2e)$ scattered electron angular distributions are strong functions of the ejected electron direction. [Preview Abstract] |
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M6.00063: Recent progress in polarization bremsstrahlung from thin-film and gas targets Ryan Haygood, Scott Williams, C.A. Quarles We are continuing to investigate polarization bremsstrahlung (PB) in both thin-film and free gas atom targets. PB has been observed in recent gas target experiments at 28 and 50 keV on Ar, Kr and Xe. These results contrast with many earlier experiments on bremsstrahlung from thin-film targets in which no PB has been observed. We report initial results of a study of the target thickness dependence of thin films to investigate whether PB is suppressed in solid targets as a function of thickness. We also report initial investigation of a background, not previously considered, that can occur with gas targets but is not significant for thin-film targets. At the energies of the gas target experiments, this background is mainly from Rayleigh scattering in the extended gas target cell of the photon spectrum produced by electron scattering into beam collimators, the Faraday cup and target chamber walls not directly seen by the detector. [Preview Abstract] |
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M6.00064: Polarized Fluorescence from Nitrogen Molecules Excited by Polarized Electron Impact J.W. Maseberg, J.E. Furst, T.J. Gay We have measured the optical excitation function and relative Stokes parameters for 388$\pm $5 nm fluorescence from spin-polarized electron impact excitation of molecular N$_{2}$. Specifically, the circular polarization fraction normalized to the incident electron spin, P$_{3}$/P$_{e}$, was found to be +1(5){\%} at an electron energy of 30eV. This result, even though it contains contributions from 6 different triplet spectral lines, is consistent with the data of the M\"{u}nster group [1] who measured the N$_{2}$ 337 nm C$_{3}\Pi _{u}$ - B$_{3}\Pi _{g }(\nu '$=0, $\nu $=0) transition and found P$_{3 }<$ 0.002 at an energy of 14.5 eV. However the N$_{2}$ results are significantly different from the H$_{2}$ target case which gives P$_{3}$/P$_{e}$ of $\sim $10{\%} [2]. [1] C. Mette \textit{et al}., Verhandl. DPG (VI) \textbf{29}, 462 (1994). [2] A.S. Green \textit{et al}., Phys. Rev. Lett. \textbf{92}, 093201 (2004). [Preview Abstract] |
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M6.00065: The Next Generation Mott Polarimeter Dennis Neufeld, F.B. Dunning New insights into many physical phenomena can be obtained through spin dependent studies and such investigations frequently require an electron spin polarimeter. In the past, polarimeters have tended to be bulky and require very high voltages (100 kV or more) in order to operate. In recent years more compact, retarding-potential designs, which operate in the 20 kV range have been developed which, with a Thorium target foil and 25 kV accelerating voltage, can achieve efficiencies of $\approx $ 1.6 x 10$^{-4}$ and effective Sherman functions, S$_{eff}$, of between --0.15 and --0.25. Here, a new ultra-compact retarding-potential polarimeter is described in that is optimized for size, efficiency, and simplicity of construction, and is suitable for a wide variety of applications. [Preview Abstract] |
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M6.00066: Electron-Impact Ionization from Excited States in H-Like Ions D.C. Griffin, C.P. Ballance, M.S. Pindzola, F. Robicheaux, S.D. Loch, J.A. Ludlow, M.C. Witthoeft, J. Colgan, C.J. Fontes, D.R. Schultz To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from such states in H, Li$^{2+}$, and B$^{4+}$ using the R-matrix with pseudo states (RMPS) and the time-dependent close-coupling (TDCC) methods. We will show comparisons of the results of our RMPS and TDCC calculations with those from our classical trajectory Monte-Carlo (CTMC) and distorted-wave (DW) calculations; these comparisons demonstrate that the CTMC method is more accurate than the DW method for H, but does not improve with $n$ and grows substantially worse with $Z$, while the DW method improves with $Z$ and grows worse with $n$. [Preview Abstract] |
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M6.00067: Calculation of Radiative and Collisional Atomic Processes G.X. Chen, K. Kirby, N.S. Brickhouse \noindent Relativistic calculations of the atomic structure of Ne\ {\sc ix} have been carried out using the multi-configuration Dirac-Fock (MCDF) method. Accurate X-ray wavelengths and transition probabilities are obtained for transitions involving levels with $n\le10$. We use several techniques to calculate accurate and consistent multipole $A$-coefficients. For example we report a transition rate of $(1.07\pm0.02)\times10^4$\ sec$^{-1}$ for the $z$ line in good agreement with the recent EBIT measurement and with previous calculations using different methods. A subset of the MCDF orbitals for $n\le5$ is used for relativistic {\sl R}-matrix calculations of electron impact excitation and recombination using the Breit-Pauli {\sl R}-matrix and the Dirac {\sl R}-matrix methods. These atomic data, together with other related data from the APED atomic database for Ne\ {\sc ix}, are used to build an extended plasma model for X-ray spectra of the Capella corona observed by the {\sl Chandra} X-ray Observatory. We offer some possible explanations for the problems in the line intensity ratios K$\beta2$/K$\beta1$ and in the inconsistency in the temperature determined by differential emission measurements. [Preview Abstract] |
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M6.00068: Effective collision strengths for electron impact excitation of doubly ionized Aluminium C.E. Hudson, K.L. Bell Effective collision strengths for the electron impact excitation of doubly ionized aluminium have been determined using the R-matrix method. The lowest 10 $LS$ states are included as targets in the expansion of the total wavefunction. The fine-structure electron collision strengths have been obtained by transforming to a $jj$-coupling scheme using the JAJOM program of Saraph (Comp. Phys. Commun. vol. 15 p. 247 (1978)) and these are determined at a sufficiently fine energy mesh to delineate properly the resonant structure. Effective collision strengths for the transitions between the resulting 17 fine structure levels have been obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities. We make comparison of our data with the $LS$ transition data from 3 other calculations - Kimura et al. (A\&AS 132, 99 (1998)), Dufton \& Kingston (J Phys B 20, 3899 (1987)) and Mitroy \& Norcross (Phys Rev A 39, 537 (1989)). Significant discrepancies exist between these three earlier works, and the current work supports the calculation of Kimura et al. [Preview Abstract] |
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M6.00069: Role of Relativistic Effects in the Ionization of Heavy Ions by Electron Impact Bidhan C. Saha, Arun K. Basak, M. Alfaz Uddin Electron impact single ionization cross sections of few heavy ions are evaluated using the recently proposed modifications [1] of the widely used simplified version of the improved binary-encounter (siBED) dipole model [2]. This model consists of two adjustable parameters and it is found that they are related to the nature of the charge distribution in the bonding region of the target. For its effective uses for ionic target the siBED model is further modified [3] in terms of the ionic and relativistic effects. This study focuses on the relativistic energy domain and the findings suggest the fate of those parameters. Details of our findings will be presented at the conference. [1] W. M. Huo, Phys. Rev. A 64, 042719 (2001). [2] M. A. Uddin, M. A. K. F. Haque, A. K. Basak and B. C. Saha, Phys. Rev A70, 0322706(2004). [3] M. a. Uddin, M. A. K. F. Haque, M. S. Mahbub, K. R. Karim, A.K. Basak and B. C. Saha, Phys. Rev. A (in press) 2005. [Preview Abstract] |
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M6.00070: On the similarity of Breit-Pauli and Dirac R-matrix collision strengths for iron peak elements: an Fe$^{14+}$ case study C.P. Ballance, K.A. Berrington, D.C. Griffin, N.R. Badnell In calculating collision strengths and excitation rates for electron impact on moderately ionized iron peak elements, an issue arises over whether the Breit-Pauli R-matrix method is sufficiently accurate as compared with the Dirac R-matrix method. We test this for Fe$^{14+}$ by removing as far as possible any variation in algorithmic features, such as the energy mesh and target state expansion used, as opposed to genuine differences between the two approaches. We find the average difference between the Breit-Pauli and Dirac R-matrix effective collision strengths is only 6\%, which confirms the hypothesis that if one gets the Dirac and Breit-Pauli target states close, and resolves the resonances adequately (we use up to 384 101 points), then the Dirac and Breit-Pauli collision strengths are in good agreement. [Preview Abstract] |
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M6.00071: Coincidence measurements of scattered projectiles, ejected electrons, and recoil ions for 1000 eV electron impact on argon Jared Gavin, Mark Thomason, Robert DuBois Coincidences between projectiles scattered in the forward direction, ejected electrons, and target ions were measured for 1000 eV electron impact on argon atoms. A position sensitive detector was used to record scattered projectiles with energy losses up to approximately 100 eV and scattering angles less than 10$^{o}$. A second position sensitive detector recorded electrons emitted from the target region between 90$^{o} \quad \pm $50$^{o}$ in the $\theta $, $\phi $ directions. Target ions were extracted through a small aperture and detected by a channeltron. This defined the collision region and from time-of-flight coincidences, the degree of ionization was determined. Positions on the projectile detector provide energy loss and scattering angle information. From positions on the electron detector plus energy loss information, the ejected electron energy and angles were determined. Examples of doubly and triply differential data will be presented and discussed. Similar studies using positron impact are in progress. [Preview Abstract] |
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M6.00072: ATOM-ATOM, ATOM-MOLECULE, AND ATOM-SURFACE COLLISIONS
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M6.00073: Electron capture scaling law in multiply charged ions – H2 collisions revisited Kevin Cornelius Single electron capture involving the system A$^{q+}$ + H$_{2}$ at intermediate to high collision energies is re-examined to incorporate the many recent advances in experimental electron capture measurements. An original study done by Berkner \textit{et}. \textit{al}. determined an empirical expression for electron capture cross sections for Fe $^{q+}$ + H$_{2}$ collisions over the energy range 275 to 3400 \textit{ke}V/$u$ and a charge $q$ range from 9 to 25. This current work examines the effect of recent data from other recent collision systems and provides an updated scaling law with the same form as the original. This updated empirical work is also compared to a capture scaling law determined from a system of collisions calculated using the classical trajectory Monte Carlo method. [Preview Abstract] |
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M6.00074: Close-Coupling study of vibrational-rotational quenching of CO by hydrogen atoms B.H. Yang, P.C. Stancil, N. Balakrishnan Accurate scattering calculations of rovibrational transitions for diatomic molecules induced by collisions of neutral species is a computationally challenging problem. In this work, quantum mechanical scattering calculations were performed for the rovibrational relaxation of CO in collisions with H atoms using the close-coupling approach for collision energies between 10$^{-5}$ and 500 cm$^{-1}$. We adopted the H-CO interaction potential of Werner, Keller, and Schinke and computed state-to-state and total cross sections for the quenching of the $v$=1, $j$=0-2 levels of CO. Numerous resonances, as a consequence of the van der Waals potential, are observed and the cross sections are found to approach the Wigner relation in the limit of zero energy. Also, by averaging the cross sections over a Boltzmann distribution of velocities of the incoming atom, the quenching rate coefficients were obtained. The results will be compared with previous calculations which usually adopted a decoupling approximation. [Preview Abstract] |
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M6.00075: Low energy He+H$_{2}$ collisions: Comparative study between two potential surfaces Teck-Ghee Lee, C. Rochow, R. Martin, T.R. Clark, R.C. Forrey, N. Balakrishnan, P.C. Stancil, A. Dalgarno, David Schultz, Gary Ferland The two most recently published potential energy surfaces (PESs) for the HeH$_{2}$ complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H$_{2}$($\nu=1, j=0$) total quenching cross section computed using the BMP potential was found to be a factor of $~$1000 larger than that obtained with the MR surface. Detailed analysis has been performed to uncover the origin of the discrepancy. [Preview Abstract] |
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M6.00076: Spin-Polarized Collisions in Metastable Rare Gases Chad Orzel, Ryan McMartin We will report progress toward a measurement of ionizing collision rates in spin-polarized samples of metastable argon and krypton. The Penning ionization (PI: $Rg^* + Rg^* \rightarrow Rg + Rg^+ + e^-$) and associative ionization (AI: $Rg^* + Rg^* \rightarrow Rg_{2}^{+} + e^-$) processes in these systems do not conserve spin; in the absence of spin-dependent interactions, these collisions should be strongly suppressed in spin-polarized samples. We will measure polarized and unpolarized collision rates using samples of laser-cooled atoms loaded into a magnetic trap. [Preview Abstract] |
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M6.00077: Electronic excitation of Na due to low-energy He collisions C. Y. Lin, B. H. Yang, P. C. Stancil, H. P. Liebermann, P. Funke, R. J. Buenker In warm astrophysical environments electron collisions are the primary mechanism for thermalizing the internal energy of ambient atoms and molecules. However, in cool stellar and planetary atmospheres, the electron abundance is extremely low so that thermalization is only possible through collisions of the dominant neutral species, H$_2$, He, and H. Typically, the neutral cross sections are much smaller than those due to electrons, so that the level populations of the atmospheric constituents may display departures from equilibrium. Unfortunately, these cross sections are generally not available for collision energies typical of stellar/planetary environments. In this work, we investigate the electronic excitation of Na due to collisions with He for energies near and just above threshold. The calculations are performed with the quantum-mechanical molecular-orbital close-coupling method utilizing ab initio adiabatic potential curves and nonadiabatic radial and rotational coupling matrix elements obtained from multireference single- and double- excitation configuration interaction approach. State-to-state cross sections and rate coefficients will be presented and compared with other theoretical and experimental data where available. [Preview Abstract] |
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M6.00078: Rovibrational quenching of rotationally-excited CO by helium T.G. Heil, P.C. Stancil, R.C. Forrey, N. Balakrishnan Collisional quenching of molecular species is an important process in a variety of astrophysical environments including interstellar clouds, photodissociation regions, and cool stellar/planetary atmospheres. Further, it may prove interesting to study molecular collisions at cold and ultra-cold temperatures as schemes are currently being developed to efficiently cool and trap neutral polar molecules. In this work, quantum mechanical scattering calculations will be presented for the rovibrational relaxation of rotationally-excited CO due to collisions with He for collision energies between 10$^{-5}$ and $\sim$500 cm$^{-1}$. The calculations were performed using the close-coupling approach and the $l$-labeled form of the coupled-states approximation. The accurate HeCO interaction potential surface of Heijmen {\it et al.} was adopted and numerical CO wave functions are utilized in the calculation of the potential coupling matrix elements. State-to-state and total cross sections for the quenching of CO will be presented with an emphasis on highly-excited initial rotational levels. Comparisons will be made to previous calculations and measurements where available. [Preview Abstract] |
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M6.00079: The effects of parrafin and drifilm coatings on the depolarization of rubidium at stainless steel surfaces Mark Rosenberry, Sean Gill, Michael Wickham Some applications of optical pumping (e.g. polarized electron generation$^{1})$ require high rubidium polarizations at low buffer gas pressures. A coated surface is clearly desirable for such applications. Furthermore the details of the relaxation mechanisms are not fully understood, despite earlier work by the groups of Bouchiat$^{2}$ and Swenson.$^{3}$ Work is in progress to fully characterize the surface effects of tetracontane and OTS coatings on stainless steel substrates to obtain depolarization time constant(s) for different temperatures and how they change with time. $^{1}$ H. Batelaan, A.S. Green, B.A. Hitt, T.J. Gay, Phys. Rev. Lett. \textbf{82}, 4216 (1999) $^{2}$ M.A. Bouchiat and J. Brossel, Comp. Rend. \textbf{254}, 3828 (1962) $^{3}$ D.R. Swenson and L.W. Anderson, Nucl. Instr. Meth B \textbf{29}, 627 (1988) [Preview Abstract] |
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M6.00080: Muon transfer from muonic hydrogen to atomic oxygen and nitrogen Anh-Thu Le, Chii-Dong Lin The results of the diabatic hyperspherical close-coupling calculations are presented for the transfer of negative muon from muonic hydrogen to oxygen and nitrogen for collision energies from 1 meV to1 keV. It is shown that converged results can be obtained using a much smaller number of channels than in the traditional adiabatic approach. For the energy range below 10 eV our results for nitrogen are in good agreement with the available experimental data and the recent calculations within hyperspherical elliptic coordinates. However, discrepancies were found in the case of oxygen, where a p-wave shape resonance is shown to contribute significantly to the cross sections. We show that for oxygen the p-wave resonance extends to a large volume and is sensitive to the many-body effect. Calculations including outer screening of the oxygen atom have been performed to illustrate the importance of such effect. [Preview Abstract] |
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M6.00081: PHOTON-MOLECULE AND PHOTON-CLUSTER INTERACTIONS
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M6.00082: Double-Slit Interference of Correlated Photoelectrons from Hydrogen Molecules K. Kreidi, R. Doerner, T. Jahnke, O. Jagutski, H. Schmidt-Boecking, Th. Weber, T. Osipov, M. H. Prior, A. Kheifets, A. Landers, C.L. Cocke We have studied the influence of the alignment and inter-nuclear separation on the electron emission from a hydrogen molecule following the absorption of a single, circularly polarized 240 eV photon. Using the COLTRIMS technique, we obtained fully differential cross sections for the double photo ionization for fixed-in-space molecular orientations by measuring the momenta of the two protons and one electron in coincidence. The measurements cover 4$\pi $ solid angle. The body-fixed electron angular distributions include the effects of diffraction, symmetry, selection rules and the molecular orientation. The patterns show, for the first time, a kind of Young's double slit interference of a correlated electron pair inside a hydrogen molecule. The distributions have a distinct and unexpected dependency on the energy sharing between the two electrons, the molecular orientation and the kinetic energy of the two protons. The experimental results are compared with quantum mechanical calculations. This work is supported by: the Deutsche Forschungsgemeinschaft, and the BMBF (Germany) and by the Chemical Sciences, Geoscience and Biosciences Div., Office of Basic Energy Sciences, Office of Science, USDOE [Preview Abstract] |
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M6.00083: Exploring the parameter space for ionization and dissociation of H$_{2}^{+}$ in an intense laser pulse Vladimir Roudnev, B.D. Esry We explore the dissociation and ionization of H$_{2}^{+}$ ions aligned with a 790~nm laser field of peak intensity in the range 1.0$\times $10$^{13}$ to 7.0$\times $10$^{14}$~W/cm$ ^{2} $. Calculated dissociation and ionization probabilities are reported for different initial vibrational states and for the initial state averaged over the Franck-Condon distribution. The dependence on the carrier-envelope phase difference for different initial states and for pulse durations from 5 to 30~fs FWHM is presented. These results --- from direct solution of the time-dependent Schr\"odinger equation --- are compared with solutions in the Born-Oppenheimer representation with two-channels for low peak laser intensities. [Preview Abstract] |
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M6.00084: Cl K$\alpha$ resonant x-ray Raman scattering from CF$_3$Cl A.C. Hudson, W.C. Stolte, R. Guillemin, O.A. Hemmers, D.W. Lindle, P.W. Langhoff Polarization dependent K$\alpha$ x-ray emission has been measured after core Cl 1{\it s} resonant excitation of gas phase CF$_3$Cl. All of these measurements in the near-threshold region show significant non-statistical polarization differences with photon energy. For photon energies above-threshold, the theoretical doublet ($\alpha$$_{1}$:$\alpha$$_{2}$ or 2$\textit{p}$$_{3/2}$:2$\textit{p}$$_{1/2}$) ratio of 2:1 is preserved but only when taking an average of the two polarization measurements. Work was partly supported by NSF grant PHY-01-40375. [Preview Abstract] |
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M6.00085: Doppler-free saturation spectroscopy of acetylene inside a photonic band-gap fiber Rajesh Thapa, Mohammed Faheem, Kristan Corwin We are developing portable frequency references based on saturated absorption of acetylene ($^{12}$C$_{2}$H$_{2})$ in the near IR spectral region with sub-MHz accuracy inside hollow core photonic band-gap fibers. Acetylene is a commonly employed reference gas in the telecommunications band. The light from the tunable diode laser at $\sim $ 1531 nm (P11) is amplified by an erbium-doped fiber amplifier (EDFA) and split into a strong pump beam and a weak probe beam which counter propagate inside the gas-filled fiber. The sub-Doppler profile appears as a narrow absorption feature, about 20-40 MHz wide, even at the low pump power of $\sim $18 mW. We also observe narrower sub-Doppler features in the 20 $\mu $m-core fiber than in the 10 $\mu $m --core fiber, consistent with the limitation of transit-time broadening. [Preview Abstract] |
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M6.00086: Photoexcitation of a Volume Plasmon in C$_{60}$ Ions R.A. Phaneuf, E.D. Emmons, M.F. Gharaibeh, A.L.D. Kilcoyne, A.S. Schlachter, S. Schippers, A. Mueller, H.S. Chakraborty, M.E. Madjet, J.M. Rost, S.W.J. Scully Neutral C$_{60}$ is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements made at the Advanced Light Source for C$_{60}^{+}$, C$_{60}^{2+}$ and C$_{60}^{3+}$ ions in the 17-75 eV energy range show an additional broad resonance near 40 eV. Time-dependent density functional theory calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry of a charged spherical shell. [Preview Abstract] |
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M6.00087: Cross-Section Ratios of Multiple-Photoionized C60 Clusters Pavle Jurani\'c, Dragan Luki\'c, Kathleen Barger, Ralf Wehlitz Relative C$_{60}^{2+}$/ C$_{60}^{+}$, C$_{60}^{3+}$/ C$_{60}^{+}$, and C$_{60}^{4+}$/ C$_{60}^{+}$ photoionization cross-sections have been obtained by using synchrotron radiation between 19 and 180 eV. The measurements were carried out at the Synchrotron Radiation Center (SRC) in Stoughton, WI, using an oven to vaporize C$_{60}$ powder and synchrotron light to photoionize the gas. In addition to procuring the above-mentioned curves, we have also observed the photoionization-induced fragmentation of C$_{60}$ at higher ($>50$ eV) photon energies. The measurements are an improvement to existing data \footnote{T.\ Drewello {\it et al.}, Int. Journal of Mass Spectrom. and Ion Processes {\bf 124}, R1 (1993).} \footnote{A.\ Reink\"oster {\it et al.}, J.\ Phys.\ B {\bf 37}, 2135 (2004).}. The C$_{60}^{2+}$/ C$_{60}^{+}$ relative cross-section curve seems to exhibit an oscillatory behavior, and the possible causes of this behavior will be discussed. [Preview Abstract] |
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M6.00088: STRONG FIELD MOLECULAR PROCESSES II
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M6.00089: Effects of Molecular Alignment on High Harmonic Generation from N$_{2 }$ in a Hollow-Core Waveguide Brett Sickmiller, Robert Jones We have studied high harmonic generation (HHG) from laser aligned N$_{2 }$molecules in a hollow-core waveguide. In the experiments, a Michelson interferometer splits a single 30 fsec 790 nm laser pulse into two time-delayed laser pulses which are then focused into a N$_{2}$ filled glass capillary tube [1]. First, the ``alignment'' pulse drives a sequence of Raman transitions within each N$_{2 }$molecule, creating a rotational wavepacket whose temporal evolution results in the periodic alignment of the molecular axis parallel (or perpendicular) to the laser polarization axis [2]. We measure the 15$^{th}$ -- 25$^{th}$ harmonics produced by the transiently aligned molecules using the second, ``signal'' laser pulse. The relative angle between the signal pulse polarization and the molecular axis is varied by changing the pulse delay or by rotating the polarization of the alignment pulse in the interferometer. We observe variations in the individual harmonic signals of up to a factor of 3 for parallel as compared to perpendicularly aligned targets. In addition, we are exploring the effects of laser-chirp and ellipticity on the HHG yield in an attempt to provide additional information regarding non-perturbative molecular dynamics in the presence of intense laser fields. This work is supported by DOE BES and the UVa FEST. [1] A. Rundquist \textit{et al}., Science \textbf{280}, 1412 (1998). [2] F. Rosca-Pruna and M.J.J. Vrakking, Phys. Rev. Lett.\textbf{ 87}, 153902 (2001). [Preview Abstract] |
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M6.00090: Strong-field ionization of dynamically aligned molecules Igor Litvinyuk, Ali Alnaser, Irina Bocharova, Chakra Maharjan, Lew Cocke In a pump-probe experiment molecules (N2, O2) were first dynamically aligned by creating coherent rotational wavepackets with a 30 fs 800 nm pump pulse, and then singly ionized by a properly delayed more intense probe pulse. The momentum distributions of electrons and ions produced by the tunneling strong-field ionization were measured for different alignments of molecular axes with respect to electric field vector. [Preview Abstract] |
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M6.00091: Precision calculations of high-order harmonic generation of H$_{2}^{+}$: time-dependent non-Hermitian Floquet approach Dmitry A. Telnov, Shih-I Chu Precision 3D calculations of high-order harmonic generation (HHG) rates of H$_{2}^{+}$ in intense 532 nm laser fields are performed [1] using the \textit{time-dependent non-Hermitian Floquet} approach recently developed [2]. The procedure involves the extension of the \textit{complex-scaling generalized pseudospectral} method for non-uniform spatial discretization of the Hamiltonian and non-Hermitian time propagation of the time-evolution operator. The HHG rates are computed at the equilibrium internuclear separation ($R = 2.0$ a.u.) and several laser intensities, as well as at the laser intensity $5\times 10^{13}$ W/cm$^{2}$ and various internuclear distances in the range between 3.0 and 17.5 a.u. At some internuclear separations $R$, the HHG productions are strongly enhanced and this phenomenon can be attributed to the resonantly enhanced multiphoton ionization at these $R$. \\ \noindent [1] D.~A.~Telnov and S.~I.~Chu, Phys.~Rev.~A \textbf{71}, 013408 (2005).\\ \noindent [2] D.~A.~Telnov and S.~I.~Chu, J.~Phys.~B \textbf{37}, 1489 (2004). [Preview Abstract] |
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M6.00092: O$_{2}^{+}$ dissociation caused by an ultrashort intense laser pulse A.M. Sayler, P.Q. Wang, J.F. Xia, M.A. Smith, R. Cabrera-Trujillo, K.D. Carnes, B.D. Esry, I. Ben-Itzhak Laser-induced dissociation of O$_{2}^{+}$ has been experimentally studied with ultrashort ($\sim $50 fs) intense (10$^{14}$ to 10$^{15}$ W/cm$^{2})$ laser pulses at 790 nm using kinematically complete coincidence 3D momentum imaging. The resulting kinetic energy release (KER) distribution has several distinct peaks, each of which has a unique angular distribution. The lower KER features are peaked around the laser polarization, while at higher KER, dissociation perpendicular to the laser polarization is significant. For comparison, a theoretical study of O$_{2}^{+}$ dissociation using the Electron-Nuclear Dynamics (END) approach with a laser pulse included in the time-dependent dynamics is underway. Preliminary results also indicate that ionization, which occurs predominantly at the high end of the intensity range, is strongly peaked along the laser polarization. [Preview Abstract] |
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M6.00093: Resonant Excitation in the Double-Ionization of O$_2$ Molecule by Intense Short Laser Pulses Ali Alnaser, M. Zamkov, C.M. Maharjan, P. Ranitovic, B. Shan, Z. Chang, I. V. Litvinyuk , C.L. Cocke The purpose of this experiment is to identify mechanisms whereby doubly charged molecules are produced by short intense laser pulses on neutral targets. We have used the COLTRIMS technique to measure in coincidence O$^+$ ion pairs produced in the double ionization of O$_2$ molecules by intense short laser pulses. High-resolution kinetic energy spectra and the angular distributions of the fragment ions were obtained. By using laser pulses of different durations (8-40 fs), intensities (1-10 X10^{14} $W/cm^2$) and wavelengths (500-2000nm), we found that double ionization of O$_2$ may occur from a combination of three different processes: Field ionization, rescattering and resonant multiphoton excitation. The production of the B$^3\Pi_g$ state in the $O_2^{2+}$ dictation shows a strong dependence on the laser wavelength. The data presented provide clear evidence of resonant multiphoton excitation in the production of the B$^3 \Pi_g$ state at 800 nm wavelength. [Preview Abstract] |
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M6.00094: ULTRA SHORT LASER PULSE PROCESSES
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M6.00095: Circularly polarized laser assisted photoionization spectra Zengxiu Zhao, Zenghu Chang, Xiaomin Tong, Chii-Dong Lin Angle-resolved photoelectron spectra of argon atoms by XUV attosecond pulses in the presence of a circularly polarized laser field are calculated to examine their dependence on the duration and the chirp of the attosecond pulses. From the calculated electron spectra, we show how to retrieve the duration and the chirp of the attosecond pulse using genetic algorithm. The method is expected to be used for characterizing the attosecond pulses which are produced by polarization gating of few-cycle left- and right-circularly polarized infrared laser pulses. [Preview Abstract] |
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M6.00096: Electron Rescattering in Optical Vortices Chad Petersen, James Strohaber, Igor Mariyenko, Cornelis Uiterwaal A well-known phenomenon in ultrafast intense-field ionization is the rescattering of electrons. It is of central importance in most currently employed techniques for the generation of attosecond pulses$^{2}$. Polarization plays an important role, with linear polarization tending to favor rescattering, while circular polarization tends to inhibit it$^{3}$. Observations of this kind have been successfully explained by assuming the electron's orbit can be calculated classically after it has been released in the initial ionization step$^{4}$. We are currently investigating if we can influence the rescattering probability using \textit{laser} \textit{optical vortices}$^{5} $. These (and other) special light modes are becoming increasingly popular in the manipulation of microscopic particles. Their effect on such particles can often be understood in terms of the transfer of \textit{optical orbital angular momentum} (optical spanner). In a separate contribution we describe our experimental efforts to create intense optical vortices of femtosecond duration. In the present contribution, we discuss trajectories of free electrons in optical vortices and other fields with exotic topologies. $^{2}$ see e.g. Z. H. Chang, \textit{Phys. Rev. A} \textbf{70,} 043802 (2004) $^{3}$ D. N. Fittinghoff \textit{et al.}, \textit{Phys. Rev. A} \textbf {49,} 2174 (1994) $^{4}$ P. B. Corkum, \textit{Phys. Rev. Lett.} \textbf{71,} 1994 (1993) $^{5}$ see e.g. L. Allen \textit {et al.}, \textit{Optical Angular Momentum} (IoP, Bristol, 2003). [Preview Abstract] |
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M6.00097: Attosecond-Time Resolved Fano Resonances M. Wickenhauser, J. Burgd\"ofer, C.D. Lin, M. Dresher, F. Krausz Recent advances in the generation of sub-fs XUV pulses and attosecond metrology have opened up the possibility to trace the time evolution of electronic wavepackets inside atoms in pump-probe experiments. We investigate the feasibility of observing the build-up of a Fano resonance in the time domain with attosecond resolution [1]. Excitation with the pump pulse opens two interfering paths from the ground state to the continuum. The time evolution of the coherent superposition of resonant state and continuum is mapped onto a modulation of the electron spectrum as a function of the time delay between pump and probe pulse. First results for super-Coster Kronig transitions with lifetimes of the order of 400 asec will be presented. \\ \noindent [1] M.\ Wickenhauser et al., PRL {\bf 94} 023002 (2005). [Preview Abstract] |
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M6.00098: Spatially Resolved Time-of-Flight Ion Mass Spectrometry with Femtosecond Pulses James Strohaber, Igor Mariyenko, Chad Petersen, Cornelis Uiterwaal When a focused laser beam is used to study intense, ultrafast ionization processes in a target gas, the interaction region (where the intensity is highest) is usually surrounded by larger regions in which the intensity is different. Collecting ions from all these regions makes the peak intensity ill-defined. To avoid this adverse so-called \textit{volume effect}, we detect ions from a small volume, limited in all three spatial dimensions. We report on our investigations of the focal topology of a 45 femtosecond pulse from an intense Ti:sapphire laser source ($\sim $2.5 mJ/pulse). Experiments and simulations will be presented demonstrating our technique of recording mass-resolved high-resolution spatial images of ion distributions in our laser focus. The technical details and limits of our approach will be discussed. Separate contributions present our plans to use the technique to investigate the effect of orbital angular momentum on rescattering ionization processes. \newline \par\noindent Work funded by NSF and in collaboration with MPQ (Munich) [Preview Abstract] |
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M6.00099: Diagnosis of a High Harmonic Beam Using COLTRIMS Predrag Ranitovic, Ali Alnaser, Chakra Maharjan, Bing Shan, Zenghu Chang, Igor Litvinyuk, Lewis Cocke We are developing an apparatus for performing time-resolved pump-probe photoelectron/photoion momentum spectroscopy experiments. The pump will be a short infrared pulse; the probe will be a soft x-ray generated by harmonic generation. The higher harmonics are generated through focusing 50 fs, 1 mJ Ti:sapphire laser pulses into argon and neon gases. We detect and measure in coincidence the momenta of the electrons and ions generated by the ionization of a diffusive argon jet gas by the harmonic beam. We use the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) technique to measure the momenta. The spectrometer electric field separates ions and electrons which are detected by time- and position-sensitive detectors. We measure the orders of the harmonics, the intensity of the each harmonic, the x-ray beam angular divergence and the total photon flux from the momenta and yields of the photoelectrons. The characteristics of the harmonic beam will be presented and discussed. This work is supported by Chemical Sciences, Geosciences and Biosciences Division, Office of Basics Energy Sciences, Office of Science, U.S. Department of Energy. [Preview Abstract] |
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M6.00100: Characterization of ultrafast hard x-ray pulses for LCLS using gas phase techniques Marcus P. Hertlein, Reinhard Kienberger, Hidehito Adaniya, Adrian Cavallieri, Benedict Feinberg, David Fritz, Timur Y Osipov, Ali Belkacem The availability of ultrafast (sub-100 fs) hard x-ray pulses (E $>$ 1000 eV) promises new experimental opportunities, but also requires new techniques for their use. The Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center (SLAC) is such a source that is expected to provide a high flux of 230 fs monochromatic x-ray photons with energy between 0.8 and 8 keV. Characterization methods for beams with such characteristics still need to be developed. We are presenting several techniques that show promise for the spatial and temporal characterization of ultrafast hard x-rays. They were developed and used at the Advanced Light Source (ALS), and will undergo further testing at the Sub-Picosecond Photon Source (SPPS) at SLAC. Our methods exploit effects such as ultrafast core-hole binding energy changes in atoms after laser excitation, and creation of energy sidebands on Auger electrons that are emitted in a laser field. We have demonstrated the usefulness of these effects on a picosecond time scale, but their use can be extended well into the femtosecond domain. We will also discuss time-of-flight techniques which offer the possibility of nondestructive x-ray spatial mode characterization. Our focus is on gas phase experiments, since they offer the possibility of nondestructive, transparent monitoring of the x-rays, leaving the main beam nearly undisturbed and available for experiments. [Preview Abstract] |
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M6.00101: ATOMIC AND MOLECULAR STRUCTURE AND PROPERTIES
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M6.00102: Loading of multiple micro-optical traps Vijayashankar Ramareddy, Peyman Ahmadi, Gil Summy Pioneering work has been done in the use of far off-resonant laser fields to create potentials to trap and manipulate neutral atoms in the last few decades. More recently multiple traps with variable separation between them have become useful for various experiments ranging from quantum information research to cold collisions and atom interferometry. We present a new method of generating a linear array of far off resonant-traps (FORTs) making use of the intensity pattern associated with the spherical aberration of a focused CO$_2$ laser beam $\left[ 1 \right]$. The spherical aberration is introduced by the lenses in the path of the laser beam. Atoms are trapped at the local maxima of the intensity pattern. We show that the separation of these micro-traps can be varied over a range of about one millimeter. The variation of the separation of these micro-traps is achieved by changing the amount of spherical aberration which is made possible by changing the CO$_2$ laser beam size on the lenses. We could load about $2 \times 10^5 - 1 \times 10^6$ atoms in these micro-traps at 70 $\mu$K. Since the spacial extent of the magneto optical trap (MOT) (from where the FORT is loaded) is limited, 2 - 3 micro-traps are realized at a time. However by changing the relative position of the MOT with respect to FORT up to 10 micro-traps are observed.\\ $\left[ 1 \right]$ P Ahmadi, V Ramareddy and G S Summy, New. J. Phys. {\bf 7}, 4 (2005). [Preview Abstract] |
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M6.00103: Constraining the Quadrupole Shift in the Mercury Ion Optical Clock W.H. Oskay, W.M. Itano, J.C. Bergquist An optical-frequency atomic clock based upon the $282~\mathrm{nm}$ $5d^{10}6s~^{2}S_{1/2} (F=0)\longrightarrow 5d^{9}6s^2~^{2}D_{5/2} (F=2,m_{F}=0)$ transition in a single $^{199}\mathrm{Hg}^+$ ion has thus far been limited in accuracy by the shift due to the interaction of the electric quadrupole moment of the $^{2}D_{5/2}$ state with stray electric field gradients. We report an experimental measurement of the $^{2}D_{5/2}$ electric quadrupole moment and compare it with theory. We performed this measurement by observing the frequency shift of the clock transition with respect to the resonance of a stable optical cavity for various applied electric field gradients. By measuring the shift without an applied gradient, we can place an upper bound on the fractional frequency error caused by an ambient field gradient. With our existing setup, this uncertainty due to the quadrupole shift should be controllable to $10^{-17}$. We discuss the error budget of the clock and implications for recent absolute measurements of the clock transition frequency. [Preview Abstract] |
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M6.00104: Measurement of the X$^{1}$\textbf{$\Sigma_{g}^{+}\to A^{1}\Sigma_{u}^{+}$of Na_{2}$} Transition Dipole Moment by Autler Townes Splitting: Comparison of Three and Four Level Excitation Schemes Peng Qi, Annie Hansson, Teodora Kirova, Li Li, Angelos Lazoudis, Ergin Ahmed, Sylvie Magnier, A. Marjatta Lyyra, Jianbing Qi We have demonstrated that narrow band CW lasers associated with moderate Rabi frequencies can be used to study coherence effects such as Electromagnetically Induced Transparency and Autler-Townes splitting in open molecular systems. These effects can be used to control molecular angular momentum alignment and to achieve magnetic sub level state selectivity. In this paper we use Autler Townes splitting to investigate the transition dipole moment between the molecular ground state and the first excited state of the sodium dimer with the cascade and inverted Y excitation schemes. Results are compared with ab initio calculations. [Preview Abstract] |
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M6.00105: Frequency-dependent polarizabilities of alkali atoms from ultraviolet through infrared spectral regions Bindiya Arora, Marianna Safronova, Charles W. Clark We present results of first-principles calculations of the frequency-dependent polarizabilities of all alkali atoms for light in the wavelength range 300-1600~nm, with particular attention to wavelengths of common infrared lasers. We parameterize our results so that they can be extended accurately to arbitrary wavelengths above 800~nm. This work is motivated by recent experiments involving simultaneous optical trapping of two different alkali species. Our data can be used to predict the oscillation frequencies of optically-trapped atoms, and particularly the ratios of frequencies of different species held in the same trap. We identify wavelengths at which two different alkali atoms have the same oscillation frequency. [Preview Abstract] |
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M6.00106: Thomson Scattering from Ultrashort and Ultraintense Laser Pulses Ju Gao Thomson scattering is a process that occurs as an electron perturbed by photons radiates back, giving off information about its own motion. With a conventional laser, this process is linear and Thomson scattering has been used as a standard tool to diagnose electron density and speed profiles. In the intense laser field, the ``photon cloud'' that dresses the electron, which carries both (ponderomotive) energy and (ponderomotive) momentum, becomes so thick that the radiation sends information about the dressed photons as well, thus reflecting the characteristics of the laser field which includes intensity, phase and pulse profile. This suggests a changed role of the electron, from being a target in the conventional Thomson scattering experiments to functioning as a potential probe for the ultra-intense and ultra-short laser pulses. In a recent publication (PRL, 93, 243001, December 2005), we analyze unique features of the Thomson scattering inside an ultra-intense and ultra-short laser field. Calculation based on classical theory provides detailed relations between the Thomson scattering and the field characteristics. In addition, we show that the symmetry of the radiation can be broken and this symmetry-breaking ties to the ``birth time'' of the electron inside the field. [Preview Abstract] |
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M6.00107: The effect of correlation on line strengths in third row elements Charlotte Froese Fischer A number of strong interactions are present in the third row elements. The well-known two configuration $2s^2 - 2p^2$ $^1\!S$ interaction in Be~I becomes a three configuration $3s^2 - 3p^2 -3d^2$ $^1\!S$ interaction in the third row. For this row, there also is a strong $3s3d -3p^2$ $^1\!D$ interaction in many $ 3s^23p^n3d$ LS or $3s3p^{n+2}$ LS states. The effect of this interaction is to introduce severe cancellation in the calculation of oscillator strengths for some states and enhancement in others when compared with Hartree-Fock values. In neutral atoms, the $3s^3p^{n+2}$ LS state often is in the continuum but already in the singly ionized element of the iso-electronic sequence both states are observed. Cancellation occurs in line strengths of the lower states which may explain the presence of some excited levels and absence of lower levels in some spectra for highly ionized elements where level identification is less complete. Results will be presented for several isoelectronic sequences. [Preview Abstract] |
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M6.00108: X-ray M-shell spectra of multiply-charged tungsten ions produced at the energy of the electron beam of 3.9 keV at the LLNL EBIT Travis Hoppe, Alla Safronova, Ulyana Safronova, Paul Neill, Cliff Harris, Peter Beiersdorfer, Greg Brown, Kevin R. Boyce, Richard Kelly, Caroline Kilbourne, Scott Porter X-ray M-shell spectra of multiply-charged tungsten ions are spectroscopically studied. These spectra were collected at the LLNL EBIT-I at the energy of the electron beam of 3.9 keV and recorded by a broad-band x-ray microcalorimeter spectrometer (XRS). The XRS covered the spectral region from 3.5 to 8 {\AA}, which represented several distinct groups of lines due to 3-4, 3-5, and 3-6 transitions. The development of spectroscopic modeling of M-shell tungsten spectra is presented. Modeling indicates that Ni-like lines dominate at this electron energy and include not only the allowed E1 transitions but also the forbidden M1 and E2 transitions. The advantage of using LLNL EBIT data for the development of M-shell diagnostics of plasmas is shown. Work was supported by DOE-NNSA/NV Cooperative Agreement DE-FC52-01NV14050. Work at LLNL was performed under the auspices of the DOE by UC-LLNL under contract W-7405-Eng-48. [Preview Abstract] |
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M6.00109: Experimental study of alkali-metal collisional line broadening for astrophysical applications Francois Shindo, James Babb, Kate Kirby, Kouichi Yoshino The visible and near infrared spectra of L- and T-type brown dwarfs exhibit prominent resonance lines of alkali-metal atoms [1]. It is expected that such features are present in the spectra of extrasolar giant planets (EGPs) [2,3]. In the cool dwarfs, the most prominent alkali-features are due to the resonance lines of Na at 590 nm and of K at 770 nm, significantly broadened by collisions with H$_{2 }$and He at temperatures around 1000 K. As this broadening is pressure and temperature sensitive, the resonance line profile can be used as a diagnostic of the atmospheric conditions of cool brown dwarfs and EGPs. To improve the data available for modeling, we have set up a spectroscopic experiment to measure absolute absorption coefficients of alkali vapors colliding with H$_{2}$ and He at relevant temperatures. Our apparatus allows us to use the ``hook'' method to determine the atom number density of the alkali element. We will discuss our first spectroscopic measurements on the absorption of potassium vapors mixed with He buffer gas. This work is supported in part by NASA grant NAG5-12751. References: [1] $^{ }$A. Burrows et al. 2002, ApJ, 573, 394 [2] S. Seager and D. D. Sasselov 2000, ApJ, 537, 916 [3] A. Sudarsky et al. 2003, ApJ, 588, 1121 [Preview Abstract] |
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M6.00110: Electron affinity of hydrogen atom and resonance state of hydrogen negative ion in screened Coulomb potentials Yew Kam Ho, Sabyasachi Kar The 2s$^{2} \quad ^{1}$S$^{e}$ autoionization resonance state of hydrogen negative ion embedded in screened Coulomb potentials is determined by calculating the density of resonance states using the stabilization method as an extension of our earlier work [1]. The Electron affinity of hydrogen atom in such potentials is also calculated. A screened Coulomb potential can be used for the Debye model in plasmas physics. A correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect between the three charge particles. The screening effect is taken care of for all pairs of the charge particles, whereas in our earlier work the screening for the electron-electron pair was not explicitly included. The calculated resonance energies and widths for various Debye parameters ranging from infinity to a small value along with the electron affinity are reported. * Support by the National Science Council of Taiwan, ROC. [1] S. Kar and Y. K. Ho,\textit{ Phys. Rev. E} \textbf{70} (2004) 066411. [Preview Abstract] |
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M6.00111: Shifts in characteristic K- and L-shell lines as temperature diagnostics for warm, dense matter Stephanie Hansen An atomic model has been developed for use as a temperature diagnostic of warm, dense matter. Starting from a Wigner-Seitz cell whose size is determined by the ion density, self-consistent solutions for non-relativistic bound and free wavefunctions, electric and chemical potentials, and average ion charge are obtained. This average atom model is then split into individual ions. The reduced screening of the nuclear charge as the neutral atoms are ionized leads to shifts in the transition energies of characteristic lines in modeled emission spectra, which could be used to determine ionization balances and estimate electron temperatures through comparison with experimental spectra. Sample calculations for K-shell Ti and Cu and L-shell Xe are presented and comparisons with emission features calculated using the relativistic multiconfiguration atomic structure code FAC are given. [Preview Abstract] |
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M6.00112: Optical spectra from Collisions of 128keV/amu O5+ projectiles on CO Kenneth Miller, Phillip Gee, Thomas Ehrenreich, Erin Seder, Quentin Kessel, Edward Pollack, Winthrop W. Smith Optical spectra in the range 400 to 800 nm from collisions of O$^{5+}$ with CO targets have been measured. Lines from atomic transitions are observed; however, the spectra are dominated by molecular emission from the CO$^{+}$ ion. These molecular lines are consistent with large cross sections for electron capture by highly charged O projectiles. The dominant molecular bands have been identified as the (A$^{2}\Pi $-X$^{2}\Sigma )$ band of the CO$^{+}$ molecular ion, which has been observed in comet tails. This research program is sponsored by NASA EPSCoR grant NCC5-601 [Preview Abstract] |
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M6.00113: High Precision Theory and Spectroscopy for $^3$He Gordon Drake, Qixue Wu, Donald Morton In previous work, a combination of theory and high precision measurements for the transition energies of $^4$He has yielded absolute ionization energies (IE) accurate to better than $\pm$1 MHz for most states except for the ground state. In the present work, these IEs are combined with accurate calculations of the isotope shift, including relativistic recoil and quantum electrodynamic corrections, to obtain similarly high precision data for the entire singly-excited spectrum of the rarer isotope $^3$He. The hyperfine structure is also calculated and compared with experiment. In most cases, the theoretical results are expected to be definitieve values that are considerably more accurate than the available experimental data. [Preview Abstract] |
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M6.00114: Magneto-optic effect near the D1 resoance of spin-polarized cold atoms Donghyun Cho, Jai Min Choi, Jang Myun Kim, Je Hyun Lee, Q-Han Park We report our study of the magneto-optic effect in a strictly linear regime on spin-polarized cold cesium atoms. Due to the low intensity and the short illumination period of the probe beam, less than 7.5\% of the sample atoms change their states by absorbing probe photons. We produce a medium of atoms at rest in either the $6S_{1/2}, F=3, m_F=0$ or $6S_{1/2}, F=3, m_F=3$ state by optically pumping atoms trapped in a magneto-optical trap. We use the $D1$ resonance with large lower and upper state hyperfine splittings as a probe transition to avoid hyperfine mixing from the Zeeman interaction. Under this idealized situation we measure the Stokes parameters in order to find the polarization rotation and circular dichroism experienced by the probe light. We find that there are qualitative differences between the results for the $m_F=0$ and $m_F=3$ cases. While dispersion and consequent Faraday rotation plays a dominant role when the atoms are in the $m_F=0$ state, it is dissipation and circular dichroism that is important when they are in the $m_F=3$ state. Similarly, while the size of the Faraday rotation and the circular dichroism for the $m_F=0$ case scales linearly with the applied magnetic field, for the $m_F=3$ case it is the shift of the probe polarization change versus frequency that is linearly proportional to the magnetic field strength. [Preview Abstract] |
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M6.00115: Nonadiabatic Coupling in the $3\,^3\Pi$ and $4\,^3\Pi$ State of NaK R.D. Miles, L. Morgus, J.P. Huennekens, A.P. Hickman The excited $3\,^3\Pi$ and $4\,^3\Pi$ electronic states of the NaK molecule exhibit an avoided crossing, leading to anomalous behavior of many features of the ro-vibrational energy levels belonging to each state. We have carried out a joint experimental and theoretical investigation of these states. Experimentally, the hyperfine structure of numerous ro-vibrational levels has been determined using the Doppler-free, perturbation-facilitated optical-optical double resonance (PFOODR) technique. Striking patterns in the data provide a sensitive probe of the electronic wave function in the various regions of the double well $3\,^3\Pi$ potential. Companion {\it ab initio} electronic structure calculations have provided adiabatic and diabatic potential curves that account for the avoided crossing. The nonadiabatic coupling between the $3\,^3\Pi$ and $4\,^3\Pi$ states can be exactly formulated in terms of the diabatic potential curves. Using the {\it ab initio} diabatic potential curves as a starting point, we used a nonlinear fitting routine to adjust the potential curves to fit the observed structure. The pertubations between the $3\,^3\Pi$ and $4\,^3\Pi$ states have been accurately reproduced. [Preview Abstract] |
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M6.00116: Fine and hyperfine structure of ro-vibrational levels of the NaK $1\,^{1,3}\!\Delta$ states near the dissociation limit A.P. Hickman, A.D. Wilkins, L. Morgus, J. Hernandez-Guzman, J.P. Huennekens Our previous high-resolution spectroscopic studies of the fine and hyperfine structure of ro-vibrational levels of the $1\,^3\!\Delta$ state of NaK have been extended to include vibrational levels up to $v = 59$, the hightest of which are within $8\,\mathrm{cm}^{-1}$ of the dissociation limit. Using the IPA method, a potential curve is determined that reproduces all measured levels ($35 \le v \le 59$) to an accuracy of $\sim 0.026\,\mathrm{cm}^{-1}$, and $C_6$ and $C_8$ coefficients have also been determined from the long range potential. The fine and hyperfine structure of the $1\,^3\!\Delta$ ro-vibrational levels has been fit using a theoretical model that treats the intermediate angular momentum coupling, leading to values $A_v$ and $b_{\mathrm{F}}$ of the spin-orbit coupling constant and the hyperfine Fermi contact constant. The measured fine and hyperfine structure for $v$ in the range $42 \le v \le 48$ exhibits anomalous behavior whose origin is believed to be the mixing between the $1\,^3\!\Delta$ and $1\,^1\!\Delta$ states. The theoretical method has been extended to treat this interaction, and the results provide an accurate representation of the complicated patterns that arise. [Preview Abstract] |
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M6.00117: A co-magnetometer-based nuclear spin gyroscope Thomas Kornack, Rajat Ghosh, Michael Romalis We describe a new atomic gyroscope based on an alkali metal--noble gas co-magnetometer. Unlike atomic and laser gyroscopes based on the Sagnac effect, nuclear spin gyroscopes do not require a large enclosed area and can be made quite compact. A high density alkali-metal magnetometer operating in a spin-exchange relaxation free (SERF) regime is used to polarize the noble gas atoms and detect their gyroscopic precession. In this arrangement it is also possible to cancel the response to the magnetic fields as well as their gradients and transients between the two atomic species, giving a clean signal proportional to the rotation. Using a K--$^3$He co-magnetometer we demonstrated rotation sensitivity of $2 \times 10^{-7}$ rad/sec/Hz$^{1/2}$. The rotation signal can be increased by an order of magnitude using Ne-21 atoms which have a smaller magnetic moment, while the fundamental limit on the gyroscope sensitivity is about $10^{-10}$ rad/sec/ Hz$^{1/2}$ for a 10 cm$^{3}$ measurement cell. We will also present data on the long-term stability of the gyroscope obtained during a search for Lorentz violation using the K--$^3$He co-magnetometer. [Preview Abstract] |
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M6.00118: Calculation of atomic properties using the non-linear coupled-cluster method Rupsi Chandra, Marianna Safronova, W.R. Johnson One high-precision method to calculate atomic properties of one- electron systems and to study parity nonconservation (PNC) in heavy atoms is the relativistic linearized coupled-cluster method that sums infinite sets of many-body perturbation theory terms. In the present formulation of this method, single and double (SD) excitations are included completely and certain classes of triple excitations are partially added. The properties of alkali-metal atoms calculated using this method have generally been found to agree very well with experiments. However, further progress in the study of fundamental symmetries in heavy atoms calls for the improvement of the current methodology. This work is aimed at the complete restoration of the non-linear coupled-cluster terms at the SD level. Among the numerous types of non-linear coupled- cluster terms, only six will contribute to the single or double all-order equations. We have derived expressions for all six of those terms, conducted the angular reduction, and modified the single and double all-order equations accordingly. Special care has been taken to ensure proper symmetry of the double excitation coefficients. Numerical evaluation of these terms is in progress. [Preview Abstract] |
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M6.00119: Progress in the search for the electron EDM using trapped molecular ions Laura Sinclair, John Bohn, Aaron Leanhardt, Patrick Maletinsky, Edmund Meyer, Russell Stutz, Eric Cornell The current limit on the electron electric dipole moment (d$_{e} $ $<$ 1.6 * 10$^{-27}$ e*cm) was set using an atomic beam of Tl \footnotemark. We have proposed the use of molecular ions trapped in a RF quadrupole trap and cooled to cryogenic temperatures with a helium buffer gas to lower this limit. This experiment should benefit from the large effective electric fields experienced by an electron in polar molecules and the long spin coherence times of trapped ions. The use of triplet delta ground state hydrides, such as HfH$^{+}$ \footnotemark , should allow us to achieve both a highly polarized sample of ions in a relatively weak (100's of V/cm) rotating electric field and a competitive EDM enhancement factor. We will outline our proposed experimental procedure and present preliminary results of helium buffer gas cooling and mass spectrometry of heavy atomic ions as a precursor to studying molecular species. \footnotetext[1]{B.C. Regan et. al., Phys. Rev. Lett. 88, 718051 (2002).} \footnotetext[2]{G. Ohanessian et. al., J. Am. Chem. Soc. 112, 7179 (1990).} [Preview Abstract] |
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M6.00120: Candidate Molecular Ions for an Electron EDM Experiment E. Meyer, L. Sinclair, R. Stutz, A. Leanhardt, E. Cornell, J. Bohn An experiment has been proposed to trap heteronuclear diatomic molecular ions to search for the electron's electric dipole moment (eEDM - see accompanying poster). In order to pick a suitable molecule many parameters must be considered, including the polarizability, rotational constant and nuclear charge of the heavy atom, as well as the expected size of the effective electric field inside the molecule. We have developed an expedient method to estimate these properties using standard molecular structure software. This method enables us to investigate a large number of possible molecules, and points us toward the most promising candidates. We have used this technique to identify as promising candidates the hydrides HfH$^+$ and PtH$^+$. [Preview Abstract] |
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M6.00121: High-precision Phase Shift Spectroscopy of the weak 1283 nm M1 Transition in a Thallium Atomic Beam R. Uhl, C.D. Bruzewicz, J.A. Kerckhoff, P.K. Majumder Using a thallium atomic beam apparatus, we are undertaking a series of laser spectroscopy measurements with the goal of providing precise, independent cross-checks on the accuracy of new calculations of parity nonconservation in thallium\footnote{M.\ Kozlov {\em et al.}, Phys Rev.\ A64,\ 053107 (2001); A.\ Derevianko, private comm.}. In our apparatus, a laser beam interacts transversely with a 2-cm-wide thallium beam of density $\sim$4x10$^{11}$ cm$^{-3}$ and reveals roughly tenfold Doppler narrowing of the absorption profile. In the current experiment we study the very weak 1283\,nm $6P_{1/2}-6P_{3/2}$ transition using an interaction region which includes high-voltage field plates and a high-finesse confocal Fabry-Perot cavity to study phase-shifts induced by interaction with the atomic beam. We seek to determine both Stark shift components, as well as the various components of the Stark-induced amplitude within this mixed M1/E2 transition.For these studies a Lasersystem with a frequency stability in the order of $\Delta \nu$=1MHz is essential. This stability is achieved by means of a a new method for laser frequency stabilization using high-resolution detection of thallium Faraday rotation in magnetic fields of a few gauss. This phase-shift detection technique is also being used in a bi-directional ring cavity interaction geometry to search for possible long-range T-violating forces in thallium. [Preview Abstract] |
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M6.00122: The Mistakes of Theory of Relativity Hu Qinggui The two different methods were adopted to prove the theory of relativity by Einstein wrong respectively. The first method, according to the relativity, the reference frame S$'$ moves at the speed v. At the time t$'$ , the length L$'$ from the point O to the point O$'$ in the reference frame S$'$ is equal to vt$'$ when observed in its own reference frame S$'$ . But for the length L from the point O to the point O$'$ in the reference frame S, when observed in its own reference frame S, it is equal to vt . But on the other hand, when the observer is in the reference frame S, according to the relativity, the length L should be equal to (1 –v2/c2)1/ 2 times short as that of L. Thus, the contradiction equation which could show the theory of relativity wrong will appear. The second method, a similar theory which is similar to the theory of relativity was set up. The only difference between the two theories is that the similar theory choices the point 1 to deduce the conclusions, but the relativity choices the point 0 to deduce the conclusions. On the end, the conclusions of the similar theory are contrary to that of the relativity. Thus, the theory of relativity was proved wrong again. After that, the opinions about the conclusions of relativity were also drawn. [Preview Abstract] |
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