Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session D1: Poster Session I |
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Room: TELUS Convention Center Macleod A, 4:00pm - 6:00pm |
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D1.00001: ULTRACOLD MATTER I |
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D1.00002: Anomalous Recombination Rates in Ultracold Plasmas Robert Fletcher, Xianli Zhang, Steven Rolston Three-body recombination, one of the major loss processes in plasmas, has been studied over a range of densities and temperatures, resulting in a widely accepted expression for the three-body recombination rate that scales as T$^{-4.5}$. We present experimental measurements of Rydberg atom formation in ultracold plasmas (T $<$ 20K) that calls this into question. By applying a pair of short (200 ns) microwave pulses at 2.4 GHz, we ionize and detect Rydberg atoms in a quasineutral ultracold xenon plasma without destroying the plasma. Varying the delay between the two pulses, we measure the refill rate of Rydberg atoms in the plasma. The observed rates are much larger than three-body recombination theory predicts using temperature measurements from prior experiment and simulation results. This implies that either the ultracold plasma temperature is much lower than previously thought, or currently accepted three-body recombination theory fails below $\sim$20K. [Preview Abstract] |
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D1.00003: Electron screening and ion temperature equilibration in ultracold plasmas Adam Denning, Scott Bergeson The dynamics of ultracold plasmas at early times are dominated by nearest-neighbor interactions. For plasmas created from photo-ionized MOT atoms, this interaction leads to disorder-induced heating and ion temperature oscillations over time scales roughly equal to $\omega_p^{-1}$. The details of this heating should contain information about how the electrons shield ions during collisions. We report measurements of ion heating vs. initial electron temperature and plasma density. Under certain conditions, the time scale for disorder induced heating increases from $\omega_p \tau$ $\sim$ 2 to 5, suggesting strong electron shielding. We present a one-dimensional model to explain these observations. [Preview Abstract] |
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D1.00004: The four body problem Seth T. Rittenhouse, Nirav P. Mehta, J.P. D'Incao, Chris H. Greene Using democratic, body fixed hyperspherical coordinates, the four fermion problem can be reduced to a set of five dimensional integrals over a physically motivated variational basis. This method accurately produces the low-lying adiabatic hyperspherical potential curves. The details of our method are presented and then used to calculate various observables relevant to current experiments in the ultra-cold BEC-BCS crossover regime. [Preview Abstract] |
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D1.00005: 2-Dimensional Compressed Magneto-Optical Trap Rahul Mhaskar, Varun Vaidya, Georg Raithel We present an experimental implementation of a two-dimensional equivalent of a Compressed Magneto-Optical Trap (C-MOT [1]). A Zeeman slower produces a beam of rubidium atoms with flux $\sim$10$^{11}$~atoms~s$^{-1}$, velocity $\sim$25~m/s, and propagation direction along the $z$-axis. The Zeeman-slowed atoms enter a magnetic field of the form ${\bf B} \approx (\alpha x, -\alpha y, 0)$ with a magnetic-field gradient $\alpha$ that increases with $z$. Four cooling laser beams intersect the atomic-beam axis in a manner that the value of $\alpha$ increases from about 10~G~cm$^{-1}$ to about 50~G~cm$^{-1}$ within the cooling region. As a result, a magneto-optic compression effect is achieved. The velocity of the extracted, compressed atomic beam can be varied via a frequency difference among the cooling beams. In contrast to pulsed C-MOTs (see Ref.~[1]), our device operates continuously, and can be used as a starting point for the preparation of continuous-wave Bose Einstein Condensates and atom lasers. Simulations comparing the two-dimensional compressed MOT with a two-dimensional MOT without compression are presented. Future directions of the experiment will be discussed. [1] W. Petrich, M. H. Anderson, J. R. Ensher, E. A. Cornell, J. Opt. Soc. Am. {\bf 11}, 1332 (1994). [Preview Abstract] |
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D1.00006: Characterization of a Rubidium Magneto-Optical Trap Wei Wen Yu, Brad Crochet, Gregory Carson, Alina Gearba Recently at the University of Southern Mississippi, rubidium atoms were cooled and trapped in a standard magneto-optical trap (MOT). A systematic characterization of the rubidium MOT in terms of the total number of trapped atoms versus several laser intensities, laser detunings, and magnetic field gradients is currently under way. The total amount of fluorescence emitted by the cold atoms is measured with a calibrated photodetector subtending a known solid angle, while a high-speed video camera connected to a computer via an image acquisition board is used to monitor the size and the shape of the atomic cloud. The first experimental results will be presented at the meeting. [Preview Abstract] |
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D1.00007: Simultaneous Loading of $^{87}$Rb and $^{85}$Rb into a Optical Trap from a MOT Anthony Gorges, David French, Jacob Roberts We report on our experimental progress in simultaneously loading both $^{87}$Rb and $^{85}$Rb from a two-species Magneto-optic Trap (MOT) into a Far Off-Resonance Optical Trap formed by a single, focused CO$_2$ laser beam. [Preview Abstract] |
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D1.00008: External control of electron temperature in ultra-cold plasmas Duncan Tate, Roy Wilson, Margaret Martei, Anders Wood In this presentation, we will discuss our progress towards achieving external control of the electron temperature and Coulomb coupling parameter of ultra-cold plasmas. The plasma is created by partial photoionization of a dense, cold sample of rubidium atoms in a MOT using a Littman dye laser (Rb density $\sim 4 \times 10^{10}$ cm$^{-3}$, temperature $\approx 100 \mu$K). At a controllable time delay, neutral atoms embedded in the plasma are excited to a specific Rydberg state by a narrow bandwidth pulsed laser. We measure the plasma electron energy spectrum as a function of delay between the lasers, as a function of the Rydberg state populated by the second laser, and as a function of Rydberg atom density. We have made progress towards quantifying and maximizing the Rydberg atom density that can be achieved by using mm-wave spectroscopy to control the evolution of a cold, dense Rydberg sample to plasma. We have also begun preliminary investigation of plasma electron temperature measurements. We are also investigating the use of a dark SPOT to increase the Rydberg density. [Preview Abstract] |
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D1.00009: Coherent Population Trapping in Quantum Gas of Fermions Andrew Robertson, Lei Jiang, Han Pu, Weiping Zhang, Hong Ling Coherent population trapping (CPT) is an important concept and a well known phenomenon in quantum optics. We generalize this concept from systems in quantum optics to systems in ultracold atomic physics. We consider a specific system, which is derived by introducing, in the usual BEC-BCS crossover model involving Feshbach resonance, an optical coupling between the ground and excited molecular states. We present the conditions under which a CPT superposition between the ground molecular BEC and the BCS pairing state can be formed. We take advantage the tunability offered by both magnetic and optical fields, and explore this superposition for the purpose of converting the BCS pairs into ground molecular BECs as well as demonstrating coherent oscillations between ground molecules and BCS atom pairs. [Preview Abstract] |
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D1.00010: Progress Towards a Quantum Gas Microscope Jonathon Gillen, Peter Unterwaditzer, Edward Su, Amy Peng, Hannes Brachmann, Waseem Bakr, Markus Greiner We will present the latest progress towards a quantum gas microscope to experimentally realize and study complex many-body quantum systems in an optical lattice of Rb87. We are developing a novel approach in which a 2D quantum gas is stored in an evanescent-wave optical surface trap. This proximity of the 2D quantum gas to an optical surface is what allows for microscopy to be used effectively for addressing of individual lattice sites. Studies of this optical system show that sub-micron resolution and single lattice site addressability can be achieved. These experiments should allow us to realize novel, strongly correlated quantum states and to study them with unprecedented control. [Preview Abstract] |
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D1.00011: Ac-Stark shift of the hyperfine levels of alkali-metal atoms Bindiya Arora, M.S. Safronova, Charles W. Clark We study the ac-Stark shift of the hyperfine levels of the Na, K, Rb and, Cs atoms in the $ns$ ground and $np$ excited states. Both scalar and tensor frequency-dependent polarizabilities are calculated. The electric-dipole matrix elements used in the evaluation of the dominant contributions to the polarizabilities are calculated using the relativistic all-order method. The particular all-order method used in this work is a linearized version of the coupled-cluster method that sums infinite sets of many-body perturbation theory terms. Our static polarizability values are found to be in good agreement with other experimental and theoretical results. We also evaluate ``magic'' wavelengths in alkali-metal atoms for which $np_{3/2}FM$ and $nsF'M'$ hyperfine sub levels have the same ac-Stark shift enabling state-insensitive optical cooling and trapping. [Preview Abstract] |
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D1.00012: Atomic coherence engineering using controllable phase-shifts: Towards a pulsed EIT-Raman lattice clock at JILA T. Zanon-Willette, A.D. Ludlow, S. Blatt, M.M. Boyd, T. Zelevinsky, G.K. Campbell, E. Arimondo, J. Ye While fermion-based optical lattice clocks have made rapid progress recently [1], it is also interesting to explore a different kind of ultra-stable optical clocks based on bosons addressed by EIT-Raman laser fields, which may lead to practical advantages. Following two recent challenging proposals [2,3], we present several possible interrogation schemes to probe the forbidden clock transition of ultracold bosonic $^{88}$Sr atoms and to control the atomic phase accumulated during pulsed interactions while cancelling ac stark shifts. Used to finely tune temporal evolution of clock states selected as qubits, these phase shifts are relevant to a new kind of high resolution experiments controlling the spin dynamics in a radiative non symmetrical $\Lambda $ configuration. We will discuss the experimental apparatus and the stabilization scheme currently under construction in order to demonstrate the EIT-Raman spectroscopy in the Lamb-Dicke regime enabled by an optical lattice. [1] M. M. Boyd \textit{et al}, Science 314, 1430 (2006). [2] R. Santra \textit{et al}, Phys. Rev. Lett. 94, 173002 (2005). [3] T. Zanon-Willette \textit{et al}, Phys. Rev. Lett 97, 233001 (2006). [Preview Abstract] |
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D1.00013: Time-dependent quantum many-body theory of identical bosons in a double well David Masiello, William Reinhardt We formulate a time-dependent multiconfigurational self-consistent field theory for identical bosons to explore the combined effects of the condensate's mean field and atomic correlation on the many-body dynamics of a double-well BEC from first principles. Our explicitly time-dependent approach includes the the underlying mean-field orbitals as well as all possible Fock-space amplitudes allowed within a certain model space as time evolving dynamical variables, and applies the time-dependent variational principle to derive well-defined equations of motion that include the full and self-consistent coupling between these variables. Due to its general formulation and rich mathematical structure, this treatment clarifies many of the principles and approximations that are found in other relevant approaches, and proves to be a powerful theoretical tool in the understanding of recent double-well BEC interference experiments performed at MIT and Heidelberg; a novel application to the interference patterns created by ballistic expansion of Schr{\"o}dinger cat states, the analog of the double slit experiment for whole condensates, is presented. [Preview Abstract] |
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D1.00014: Measurement of the temperature dependence of the Casimir-Polder force Robert Wild, John Obrecht, Mauro Antezza, Lev Pitaevskii, Sandro Stringari, Eric Cornell The Casimir-Polder force characterizes the surface-atom force originating from fluctuations of the electromagnetic field. Theoretical work by the Trento team has focused on the temperature dependence of this force. When the temperature of the surface differs from the temperature of free space, the force is predicted to decay more slowly at large distances and to exhibit a stronger temperature dependence. By positioning a Rb-87 Bose-Einstein condensate a few microns from a dielectric surface, the JILA team has observed changes in the collective oscillation frequency that result from the spatial variations in the force. To characterize the surface, we have developed a new technique to measure the magnitude and direction of small electric field gradients with trapped neutral atoms. These gradients are measured by resonantly driving a dipole oscillation in the BEC. The oscillation growth rate provides information about the magnitude and the sign of the surface field gradient. Measurements agree with the theoretical predictions, marking the first conclusive demonstration of the temperature dependence of the Casimir-Polder force. [Preview Abstract] |
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D1.00015: Heating of a BEC by mechanical perturbation Tod Wright, Rob Ballagh, Crispin Gardiner, Ashton Bradley, Blair Blakie We present a model of condensate stirring within the truncated Wigner formalism. A condensate initially at $\mathrm{T}\!=\!0$ is perturbed by a rotating elliptical trapping potential, simulated using a novel numerical algorithm which perfectly conserves condensate band population and (rotating-frame) energy. We discuss the thermalisation of the condensate band and the relation to vortex nucleation, and contrast the results and their interpretation with those of earlier classical field treatments of the stirred-condensate system. [Preview Abstract] |
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D1.00016: BEC apparatus for optical lattice experiments Rebekah Schiller, Stephan Albert, Daniel Pertot, David Sproles, Daniel Greif, Azure Hansen, Dominik Schneble We report our progress on a BEC transporter apparatus for experiments with ultracold atomic gases in optical lattices. Using a moving-coil quadrupole magnetic trap, laser-cooled clouds of $^{87}$Rb atoms are transported along a 2D path into a glass cell. For evaporation, a TOP trap geometry is used which incorporates the quadrupole coils and affords large optical access for subsequent optical trapping and manipulation. We will discuss our experimental setup and recent results. [Preview Abstract] |
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D1.00017: ABSTRACT WITHDRAWN |
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D1.00018: A phase-space analysis of cavity assisted photoassociation of quantum degenerate molecules Markku Jaaskelainen, Christopher Search, Jaeyoon Jeong, Ivana Djuric We study the photo-association of Bose-Einstein condensed atoms into molecules using a quantized cavity field. The semiclassical stationary solutions for the three nonlinearly coupled bosonic fields are found and their stability and scaling properties in terms of physical parameters are determined. The full quantum dynamics are simulated using the positive-P distribution and a reduced dynamics in terms of molecule fraction and relative phase between atoms and molecules, which can be mapped onto a Bloch-sphere. Quantum effects at the cross over from stable steady state behavior to large amplitude nonlinear Rabi-oscillations as a function of particle number and inter-particle interaction strengths are investigated. [Preview Abstract] |
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D1.00019: Studies of Ultracold Collisions in $^{86}$Sr and $^{88}$Sr P.G. Mickelson, Y.N. Martinez, S.B. Nagel, T.C. Killian We survey recent experiments with ultracold strontium performed in our group. Trapping and cooling occurs in three stages: successive magneto-optical traps (MOTs) operating on the 461 nm and 689 nm transitions of strontium, respectively, are loaded to cool atoms to a temperature of 1 $\mu$K. Finally, atoms are loaded into a far-off-resonance optical dipole trap. Photoassociation spectroscopy near the 461 nm line is performed directly in the 689 nm MOT, while other photoassociation experiments make use of the optical dipole trap. Various experiments reveal interesting physics of ultracold collisions in strontium. [Preview Abstract] |
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D1.00020: Ultracold collisions between atoms and molecules in high vibrational states: effect of the atom-atom scattering length Goulven Qu\'em\'ener, Pascal Honvault, Jean-Michel Launay Recently, Bose-Einstein condensates of $^6$Li$_2$ and $^{40}$K$_2$ molecules have been produced using Feshbach resonances and Pauli blocking mechanism. In these experiments, molecules are formed in the highest vibrational state and composed by fermionic atoms, and the atom-atom scattering length is large and positive. Up to now, a few quantum-mechanical studies of molecular collisions in the ultralow energy range have been published [1]. Using a quantum-mechanical formalism based on hyperspherical coordinates, we have obtained elastic and inelastic rates coefficients for the fermionic system $^6$Li + $^6$Li$_2$ and for the bosonic systems $^7$Li + $^7$Li$_2$ and Na + Na$_2$ when the molecule is in a high vibrational state. We will also explain the Pauli blocking mechanism that occurs in the experiments, by comparing rates coefficients for a system composed of bosonic or fermionic atoms when the diatom is in the last vibrational state or not and when the atom-atom scattering length is increasing. \footnotesize{ [1] G. Qu\'{e}m\'{e}ner, P. Honvault, J.-M. Launay, P. Sold\'{a} n, D. E. Potter, J. M. Hutson, {\it Phys. Rev. A} {\bf 71}, 032722 (2005), and references therein } [Preview Abstract] |
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D1.00021: Ultracold atom-molecule and molecule-molecule collisions Goulven Qu\'em\'ener, T.J. Dhilip Kumar, Balakrishnan Naduvalath, Teck-Ghee Lee, Roman Krems Recent success in cooling and trapping of molecules has attracted much attention on cold and ultracold molecular collisions as well as controlled chemistry. Here we report on our progress on atom-molecule and molecule-molecule collisions in the ultracold regime. The F+HCl/DCl systems are investigated to study the effect of long-range interaction, tunneling, and rotational excitation of the molecule on chemical reactivity. The H$_2$-H$_2$ system is used as a prototype for the study of rotational and vibrational transitions in molecule-molecule collisions at ultracold temperatures. We will present results of reactive and nonreactive scattering on these systems including the relaxation of vibrationally excited H$_2$ molecules. [Preview Abstract] |
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D1.00022: Stark mixing under full interaction in ion-Rydberg atom cold collisions Raymond Flannery, Goutham Balaraman A molecular dynamics simulation technique was developed to determine Stark mixing transitions, $n\ell\rightarrow n \ell'$, in Rydberg atoms. The full ion-Rydberg atom interaction could therefore be employed. The transition probabilities were compared with the previous exact analytical results which are appropriate only to the ion-dipole interaction. The effect of higher-order multipoles could therefore be assessed. It is shown that the full interaction becomes important at extremely low incident speeds $v$ and small-intermediate impact parameters $b$. This importance is illustrated via various contour plots in the $b,v$-plane. [Preview Abstract] |
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D1.00023: Cold and ultracold dipole-dipole collisions Catherine Newell, Michael Cavagnero, Vladimir Roudnev, John Bohn Elastic collisions of ideal oriented dipoles are calculated using a variety of techniques appropriate to different cold and ultracold regimes of temperature. The elastic scattering cross section for two electric dipoles with moment $\vec\mu$ in an electric field $\vec E$ is obtained in the semi-classical Eikonal approximation, giving an exact result, $(4\pi\mu^2 /v)[1-(\hat k_i\cdot\hat E)^2]$, where $\vec k_i = m\vec v$ is the incident relative momentum. This result is expected to apply to collisions at temperatures above a few $\mu K$, encompassing recent experiments in the trapping and cooling of polar molecular gases. The Eikonal calculation contrasts sharply with the Born approximation which predicts an energy-independent cross section scaling as $\mu^4$ and which should be applicable at lower temperatures. A separate analysis of the threshold ultracold region is also presented. Numerical close-coupling results connect these various approximation methods, and demonstrate that the crossover between semi-classical and perturbative regimes occurs at the characteristic dipole energy scale, $E_0 = \hbar^6/m^3\mu^4$. [Preview Abstract] |
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D1.00024: Measurements of Electron Temperature and Density, in an AC Pulsed Oxygen Plasma Discharge Farook Yousif, Horacio Martinez, Fermin Castillo Emission and analytical spectroscopy was applied to investigate O$_{2}$ plasma, which was generated by an AC discharge between 0.15 and 0.5 Torr pressure. For the diagnostic study, a double Langmuir probe was employed. The derivation of plasma parameters is based on a theoretical description of the double-probe current-voltage characterization in the Thick Sheath Limit (TSL) region [1]. Electron temperature of $T_{e}$ = 1.09 eV and an ion density of $n_{i}$= 2.08 x 10$^{10}$ cm$^{-3}$ were evaluated at 2 Torr. We present electron temperature and ion density as a function of the pressure at 3 different power discharge levels. Also we present emission spectroscopy in the wavelength range of 200-1100 nm as a function of the pressure. \newline \newline [1] J.D. Swift and J. R. Schwar, Electric Probes for Plasma Diagnostics (New York: Elsevier) 1971. [Preview Abstract] |
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D1.00025: Landau Paradigm and Universal Properties of Heavy-Fermion Metals Miron Amusia, Alfred Msezane, Vasily Shaginyan We show that the main universal features of the low temperature - magnetic filed experimental T-H phase diagram of the heavy-fermion metal CeCoIn5 and other heavy-fermion metals can be well explained using the Landau paradigm of quasiparticles and order parameters. The main point of our theory is that quasiparticles form fermion-condensate state, achieved by a fermion condensation quantum phase transition (FCQPT). When the system of quasiparticles undergoes FCQPT, the fluctuations accompanying its quantum critical point are strongly suppressed and cannot destroy the quasiparticles. We present for the first time theoretical description of the whole phase diagram of CeCoIn5 including the change of the second order superconducting phase transition to the first-order one under the application of magnetic field. We analyze dynamic conduction recently obtained in measurements on CeCoIn5 and show that the particle-hole symmetry is violated in this metal making both the differential tunneling conductivity and dynamic conduction an asymmetric function of applied voltage. Our description of CeCoIn5 based on the Landau paradigm and FCQPT is in good agreement with facts. [Preview Abstract] |
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D1.00026: Superfluidity in a three component Fermi gas in a harmonic trap Tomi Paananen, Jani-Petri Martikainen, P\"aivi T\"orm\"a Superfluidity in a two component Fermi gas has been very recently achieved experimentally. However, a three component Fermi gas is also experimentally realistic in the very near future and has, until now, achieved only scant attention. We study ultracold three component Fermi gas in a harmonic trap. Components are different fermionic alkali atoms and they interact through s-wave interactions. There can be several different superfluid phases in the trap. These phases correspond to different pairing channels in the three component system. We show that these different phases can co-exist in a trap. Furhermore, by calculating the Gorkov correction caused by the induced interactions, we show that the many-body corrections to the mean-field theory are more pronounced for unequal mass fermion mixtures [Preview Abstract] |
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D1.00027: MONATOMIC, DIATOMIC, & MOLECULAR STRUCTURE |
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D1.00028: Signature of Quantum Interference in Photorecombination of Ar-Like Ions D. Nikoli\'c, T.W. Gorczyca, D.W. Savin, N.R. Badnell We analyze both experimental (Schippers {\it et al.}, J.~Phys.~B {\bf 31}, 4873 (1998); Phys.~Rev.~A {\bf 65}, 042723 (2002)) and calculated total cross sections for dielectronic recombination (DR) of Ar-like Sc$^{3+}$ and Ti$^{4+}$ ions in the vicinity of the $3p^{5}3d^{2}$ and $3p^{5}3d4s$ doubly-excited, highly-correlated resonances. Our R-matrix approach provides a unified quantum-mechanical description of the electron-ion photorecombination (PR) process, treating radiative recombination and DR as coherently interfering pathways for the rare asymmetric profiles of the strong $3p^{5}3d^{2}$ $^{2}F_{7/2,5/2}$ near-threshold resonances. In order to treat the PR completely and more practically, all additional (Lorentzian) resonance contributions for the rest of the Rydberg series are calculated within an independent-processes, isolated-resonance, distorted-wave approximation using the atomic structure and collision code AUTOSTRUCTURE. [Preview Abstract] |
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D1.00029: Dielectronic Recombination of Al-Like Sulfur Sh. A. Abdel-Naby, D. Nikoli\'c, T.W. Gorczyca, N.R. Badnell, D.W. Savin Accurate dielectronic recombination (DR) data are important for cosmic and laboratory plasma modeling. Over the past few years, our group has computed reliable DR data for all isoelectronic sequences up through Mg-like ions. Recently, we have focused our work on the complex third-row M-shell isoelectronic sequences. Al-like Fe$^{13+}$ DR calculations have been completed and tested against Heidelberg heavy-ion Test Storage Ring facility measurements. We extend our efforts for Al-like systems to S$^{3+}$. Although previous calculations on S$^{3+}$ exist, they were performed only within a non-relativistic LS-coupling approximation. Here we present DR rate coefficients for Al-like S$^{3+}$ using the level-resolved, multi-configurational, distorted-wave AUTOSTRUCTURE package. In order to describe the S$^{3+}$ target accurately, we extended the basis configurations previously used in Al-like Fe$^{13+}$. New results will be presented, and comparisons against available data will be shown. [Preview Abstract] |
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D1.00030: K-shell Fluorescence Yields of Li- to F-like Ions S.T. Manson, M.F. Hasoglu, T.W. Gorczyca, N.R. Badnell, D.W. Savin We have investigated the accuracy of the commonly-used fluorescence/Auger database. These data were determined from configuration average, LS, singly-charged atomic physics calculations and were then scaled up through Z=30 for all isoelectronic sequences through the iron peak elements. We have carried out new calculations, using the AUTOSTRUCTURE package, and demonstrate the significance of including properly such physical effects as correct configuration averaging (CA), semi-relativistic (i.e., spin-orbit) effects, and the previously-overlooked need to tailor the CA itself to the specific physical process of interest, showing that the extant database includes significant inaccuracies. Finally, we have completed an investigation of the isoelectronic sequences of all second-row ions. This work was supported in part by NASA APRA and SHP SR\&T programs. [Preview Abstract] |
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D1.00031: Study of dynamics of Rabi oscillation under a pulsed perturbation using hyperfine transition of trapped cesium atoms Jai Min Choi, Gee-Na Kim, D. Cho We study dynamics of Rabi oscillation under a periodic pulsed perturbation. We study how the resonance frequency of a cesium ground hyperfine transition between sublevels with nonzero magnetic quantum number is affected by periodically applied magnetic pulses. When the pulse height and pulse duration are set such that a fictitious spin completes a 2$\pi $ or its integer multiple precession around the principal quantization axis, there is no frequency shift [1]. We carry out the experiment using spin-polarized cesium atoms trapped in a magneto-optical trap. This has an important implication for metrological application of atoms trapped in an optical trap, where a systematic frequency shift and inhomogeneous broadening due to an ac Stark shift limits accuracy and precision. Our method is complimentary to the ones using a magic wavelength in a multi-level configuration [2-4] or a polarization dependence of the ac Stark shift to compensate for the differential ac Stark shift [5]. \newline [1] J M Choi, G N Kim, C. I. Sukenik and D. Cho, J. Korea Phys. Soc. submitted (2007)\, [2] Ji Yeon Kim and D. Cho, J. Korean Phys. Soc. \textbf{37}, 744 (2000)\, [3] D. Cho \textit{et al}, J. Korean Phys. Soc. \textbf{42}, 483 (2003)\, [4] Mckeer J, Boca A, Brooze A D and Kimble H J, Nature \textbf{425}, 268 (2003) [5] J M Choi and D. Cho, \textit{Proc. Int. Conf. in India}, submitted (2007) [Preview Abstract] |
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D1.00032: Third-order relativistic many-body calculation of matrix elements for divalent systems Dansha Jiang, Rupsi Pal, Marianna Safronova Third-order relativistic many-body perturbation theory (MBPT) formulas for the calculation of the transition matrix elements in systems with two valence electrons are derived. The two-particle contributions are identified among 162 third- order Goldstone diagrams and organized into 17 terms. The one-particle contributions are identical to the previously studied third-order terms in monovalent systems. Complete angular reductions of the third-order amplitudes are given. The model potential is taken to be the Dirac-Hartree- Fock (DHF) potential $V^{(N-2)}$ of the closed core. We use B-splines to generate a complete set of DHF basis orbitals for the numerical evaluation of the perturbation theory terms. The effect of the Breit interaction is also investigated. The preliminary results of the third-order calculations are presented for selected systems. Comparisons are made with second-order MBPT results, and with other calculations. [Preview Abstract] |
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D1.00033: A DFT approach for the accurate calculation of triply excited hollow and doubly-hollow Rydberg resonances in lithium isoelectronic sequence Amlan Kusum Roy Density functional calculations are performed for the $2l2l'nl'' (n \ge 2)$ triply excited \emph{hollow} resonances in lithium isoelectronic sequence. An amalgamation of the local nonvariational work-function-based exchange potential and LYP correlation functional is used. Radial KS equation is solved accurately through the Generalized pseudospectral method, leading to a nonuniform and optimal spatial discretization. Results are presented on the excited-state energy, excitation energy, radial density and other expectation values. A large number of states are studied, covering low, moderately-high and high-lying excitations, with $n$ \emph{as high as up to 25}, having varied symmetries and multiplicities. Companion calculations are made for the $3l3l'nl'' (n \ge 3)$ \emph{doubly-hollow} states of Li in the photon energy range of 176-181 eV. Detailed comparisons with recent theoretical and experimental results show excellent agreement. Many \emph{new} resonances are presented for the first time, which can provide useful guidelines for future studies. This provides a simple, efficient and general scheme for reliable and accurate treatment of multiply excited Rydberg resonances in atoms within DFT. [Preview Abstract] |
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D1.00034: B-splines in variational atomic structure theory Charlotte Froese Fischer Many of the problems associated with the use of finite differences for the solution of variational Hartree-Fock or Dirac-Hartree-Fock equations are related to the orthogonality requirement and the need for node counting to control the computed solution of a two-point boundary value problem with many solutions. By expanding radial functions in a B-spline basis, the differential equations can be replaced by non-linear systems of equations of eigenvalue type. Hartree-Fock orbitals become solutions of generalized eigenvalue problems where orthogonality requirements can be dealt with through projection operators applied to the matrix that preserve the symmetry of the matrix. When expressed as banded systems of equations, all orbitals may be improved simultaneously using singular value decomposition or the Newton-Raphson method for faster convergence. Computational procedures will be outlined for non-relativistic multiconfiguration Hartree-Fock variational methods and extensions to the calculation of Rydberg series. It will also be shown how tensor products of B-splines can be applied to the calculation of two-electron pair-correlation functions where high-order partial waves improve the short-range electron-electron cusp condition at ${\bf r_1 = r_2}$. [Preview Abstract] |
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D1.00035: Atomic Spectra Bibliography Databases at NIST A.E. Kramida In June 2006, our Atomic Spectroscopy Data Center released three new Bibliographic Databases (BD) containing references to papers with atomic data for controlled fusion research, modeling and diagnostics of astrophysical and terrestrial plasmas, and fundamental properties of electronic spectra of atoms and ions. The NIST Atomic Energy Levels and Spectra BD (http://physics.nist.gov/elevbib) [EL] is the first online version of the NIST bibliography on atomic energy levels and spectra, last published on paper in 1985. It includes more than 9300 references, mostly for years 1967 through 2004. Work is in progress to cover the latest years. The NIST Atomic Transition Probability BD, v.~8.1 (http://physics.nist.gov/fvalbib) [TP] with its 7200 references mainly covers years 1964 through 2006. The NIST Spectral Line Broadening BD, v.~2.0 (http://physics.nist.gov/linebrbib) [LB] has 3600 references, mostly for 1978 through 2006. It is a major upgrade of v.~1.0, which had only 800 references. All three databases are now maintained in a unified database management system that allows us to quickly update the contents. Updates become available to users on the next day. A new Data Entry module makes it easy to enter and categorize the data. This work is supported in part by the Office of Fusion Energy Sciences of the U.S. Department of Energy [Preview Abstract] |
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D1.00036: Balmer Line Broadening in Laser Produced Hydrogen Plasma. Lutz Huwel, Roland Volkl, Yudhishthir Kandel Photoionized plasmas have been created in hydrogen by focusing a 10 ns, 20 Hz, 1064 nm Nd:YAG laser pulse into gas that is at a pressure of 10$^{5 }$Pa. At the focus, the laser power density is about 10$^{11}$ W/cm$^{2}$. The afterglow of these plasmas has been studied with a gated, intensified CCD camera in conjunction with a 0.6m monochromator. Time and spatially resolved light corresponding to the Balmer series has been observed from excited states with principal quantum numbers up to n = 11. Detectable emission occurred up to about 4 $\mu $s after plasma creation. The observed lines are heavily Stark broadened due to the plasma environment. Analysis of the spectral lines yields information on local excitation temperature and electron density. In particular, line widths of the highly excited lines have been compared with recent theoretical predictions. A detailed discussion of the findings will be presented. We will also present results of measurements concerning the influence on the hydrogen Balmer lines in such plasmas due to the addition of inert gases such as helium and argon. $^{1}$J. E. Toumaa, E. A. Oks, S. Alexioua and A. Derevianko, \textit{Review of the advanced generalized theory for Stark broadening of hydrogen lines in plasmas with tables}, J Quant Spectrosc Rad Trans \textbf{65} 543-571 (2000) [Preview Abstract] |
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D1.00037: Relativistic many-body calculations of the energies of n=4 states for zinc-like ions Walter Johnson, Steven Blundell, Ulyana Safronova Energies of the 44 even-parity and 40 odd-parity ($4l4l'$) states of ions of the zinc isoelectronic sequence are evaluated through second order in relativistic many-body perturbation theory. Our calculations start from a Ni-like $V^{(N-2)}$ Dirac-Fock potential. Two alternative treatments of the Breit interaction are investigated. In the first version, we omit Breit contributions to the Dirac-Fock potential and evaluate Coulomb and Breit-Coulomb corrections through second order perturbatively. This version was used previously to evaluate energies Be-, B-, Mg-, Yb-like systems. In the second version, we include both Coulomb and Breit contributions to the Dirac-Fock potential and then treat the residual Breit and Coulomb interactions perturbatively. Results obtained from the two versions are compared and discussed. Theoretical excitation energies are compared with critically evaluated experimental data and with results from other recent calculations. Trends of excitation energies including splitting of triplet terms as functions of nuclear charge $Z$ = 34--100 are illustrated graphically for some states. The resulting $Z$-dependence shows explicitly the effect of mixing [$4p^2$ + $4s4d$], [$4d^2$ + $4p4df$], and [$4p4d$ + $4s4f$] configurations. [Preview Abstract] |
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D1.00038: Excitation energies, polarizabilities, multipole transition rates, and lifetimes for francium-like ions Walter Johnson, Ulyana Safronova, Marianna Safronova Energies of 7s, 7p, 6d, and 5f states in Fr-like ions with nuclear charges Z = 87 - 100 are evaluated using relativistic many-body perturbation theory complete through third order. Reduced matrix elements, oscillator strengths, and transition rates are evaluated for the 7s-7p, 7p-6d, and 6d-5f electric-dipole transitions. Multipole matrix elements for 7s-6d, 7s-5f, and 5f-5f$^\prime$ transitions are evaluated to determine lifetimes of low-lying excited states. Energies, lifetimes, and transition matrix elements for ions Z = 87 - 92 are also evaluated using the relativistic single-double (SD) method, where single and double excitations of Dirac-Fock wave functions are iterated to all orders in perturbation theory. Ground state scalar polarizabilities in Fr~I, Ra~II, Ac~III, and Th~IV are evaluated using both third-order and all-order methods. [Preview Abstract] |
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D1.00039: Isotope Shifts and Fine Structures of $^{6,7}$Li D Lines and Determination of Relative Nuclear Charge Radius. George Noble, William van Wijngaarden The $^{6,7}$Li D lines were excited using an electro-optically modulated CW dye laser that intersected an atomic beam. Fluorescence was recorded as the laser was scanned across the resonance. Hence, each transition was multiply excited allowing for calibration of the frequency scan. The $^{6,7}$Li 2P fine structures were found to be 10052.964 $\pm $ 0.050 and 10053.119 $\pm $ 0.058 MHz. The D1 and D2 isotope shifts were determined to be 10534.039 $\pm $ 0.070 and 10534.194 $\pm $ 0.104 MHz. The latter imply values for the $^{6,7}$Li relative nuclear charge radius that are within 20 millifermi of each other which is consistent with the estimated uncertainties. [Preview Abstract] |
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D1.00040: Anisotropy Dependent Circular Polarization Spectra in Cs $6p^{2}P_{3/2}$ level Burcin Bayram, Ramesh Marhatta, Jacob Hinkle, Prakash Koirala Experimental investigation of the cesium $6s^{2}S_{1/2} \rightarrow 10s^{2}S_{1/2}$ two-photon circular polarization spectra has been made. The time evolution of anisotropies, namely orientation and alignment state multipoles, in the excited state and their effects to the circular polarization spectra have been shown. Collisions between the excited level cesium atoms and the ground level argon atoms in the gas phase yielded anisotropy dependent depolarization cross section to be extracted from the measured circular polarization degree. Experimental details and the results will be presented. [Preview Abstract] |
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D1.00041: A grid-based DFT method for the electronic structure calculation of many-electron systems Amlan K. Roy, Shih-I. Chu We propose a new simple pseudopotential density functional method along with its implementation for the efficient and accurate treatment of electronic properties of molecules. The atom-centered localized gaussian basis sets, the electronic density as well as the various potentials are directly set up in a real uniform grid of three-dimensional cubic box. The nonrelativistic Kohn-Sham equation is solved within a linear combination of atomic orbitals-molecular orbitals (LCAO-MO) framework on grid using the standard self- consistent procedure. As a first step, simple local XC functionals and Hay-Wadt-type pseudopotentials are employed. As an illustration, we compare the total energy, eigenvalue, potential energy curve, the equilibrium bond length and vibrational frequency for Cl$_2$ and HCl molecule, which show very good agreement with the reference data. This provides a simple practical route to accurate molecular quantum mechanical calculations. [Preview Abstract] |
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D1.00042: Theoretical Fit fo Experimental Observations of Energy Level Structure in the Cs$_{2}$ $a ^{3}\Sigma_{u}^{+}$ State T. Bergeman, S. Sainis, E. Tiesinga, D. DeMille Precision measurements [1] on 27 hyperfine/rotational levels from 6 vibrational levels of the Cs$_{2}$ $a ^{3}\Sigma_{u}^{+}$ state, with binding energies as large as 50 cm$^{-1}$, have been performed. The objective is to identify suitable transitions to probe the energy difference between a level of a shallow bound state ($a$) and a level of a more deeply bound state ($X ^{1}\Sigma_{g}^{+}$) to be used ultimately to study the time variation of the electron to proton mass ratio [2]. It is therefore important to characterize the singlet-triplet ($X-a$) mixing due to hyperfine interactions. We have modeled the energy level structure by using a Hund's case $e$ asymptotic representation for the hyperfine interaction and rotational energy, and a case $a$ representation for the Born-Oppenheimer potentials and second-order spin-orbit (SO) interactions, with transformations between the two representations. Potentials and SO effects are adjusted to optimally fit the data. Currently, the rms residual from the fit is about twice the 30 MHz uncertainty for energy differences within each vibrational level.\\ 1. S. Sainis, Ph. D. Thesis, Yale U., 2005.\\ 2. D. DeMille {\it et al}., to be published. [Preview Abstract] |
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D1.00043: Newly observed rovibrational levels of the 3 and 4$^{1}\Sigma _u^+$ states in molecular hydrogen Aaron Marks, Joe Croman, Robert Ekey Jr., Elizabeth McCormack Double resonance spectroscopy via the $EF^{1}\Sigma_g^+, v'_{EF} =6,J'$ state has been used to probe the rovibrational structure of the \textit{ungerade} double-well $B"\overline B $(3)$^{1}\Sigma_u^+$ state of H$_{2}$. Many transitions have been observed for the first time by detecting both molecular and atomic ion production as a function of energy by using a time-of-flight mass spectrometer. Rovibrational states with $J$ = 0-4 and $v$ = 50 up to the $n$ = 3 dissociation limit are reported. A comparison of the experimentally determined and theoretically calculated rotational constants using the latest set of \textit{ab initio} molecular potentials is presented. In addition, transitions to the 4$^{1}\Sigma_u^+ v=10,J$ state, the next electronic state in the series, have been observed for the first time and term energies are reported. The double-well $^{1}\Sigma_u^+$ states are of interest because they have unusually large internuclear separation, and while many levels lie above the ionization potential, they remain extremely stable against autoionization. The new energy measurements presented here provide significant constraints on \textit{ab initio} calculations of the $^{1}\Sigma_u^+$ series in this fundamental system. [Preview Abstract] |
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D1.00044: A continuous molecular beam source of lead monofluoride P. Sivakumar, C.P. McRaven, N.E. Shafer-Ray Due to its insensitivity to background magnetic fields combined with large internal electric fields, the ground-state of lead monofluoride (PbF) may be uniquely sensitive to an electron electric dipole moment (PRA, 73, 034102, 2006). The serendipitous discovery of MgF2 and Pb yielding PbF has enabled us to build a reliable continuous molecular beam source of lead monofluoride. Details of the source and detection of the molecule are presented. [Preview Abstract] |
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D1.00045: ABSTRACT HAS BEEN MOVED TO C6.00013 |
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D1.00046: First results from the CLS far-infrared beamline: the $\nu_{12}$ and $\nu_{17}$ bands of acrolein, CH$_{2}$CHCHO Dennis Tokaryk, A. Robert McKellar, Li-Hong Xu, Dominique Appadoo, Tim May Synchrotron radiation from the new Canadian Light Source facility has been used to obtain a high resolution (0.0012 cm$^{-1})$ absorption spectrum of acrolein vapor in the 550-660 cm$^{-1}$ region. Almost 2000 transitions have been included in a detailed analysis of the $\nu_{12} $ ($\sim $564 cm$^{-1})$ and $\nu_{17} $ ($\sim $593 cm$^{-1})$ fundamental bands, yielding precise values for the band origins, rotational and centrifugal distortion parameters. The analysis included the a- and b-type Coriolis interactions connecting $\nu_{12} $ and $\nu_{17} $, as well as an a-type Coriolis interaction between $\nu_{17} $ and a ``dark'' perturbing state, identified as 4$\nu_{18} $. We believe that this is the first high-resolution infrared study of acrolein. [Preview Abstract] |
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D1.00047: Geometric Phase for Polar Molecules in rotating Electric and Magnetic Fields Edmund Meyer, Russell Stutz, Laura Sinclair, Aaron Leanhardt, Eric Cornell, John Bohn Berry's original formulation of the geometric phase [1] considered adiabatic transport of a structure-less spin by a magnetic field around a closed circuit, and found an additional phase of geometric origin. We have generalized Berry's notion to structured atoms and molecules, where different constituents contribute differently to the net magnetic and electric dipole moments. In particular, we present numerical simulations describing the geometric phase gained by a paramagnetic, polar molecule in simultaneous magnetic and electric fields. Of particular interest is the behavior of the geometric phase as the fields span the intermediate range between ``low'' and ``high'', as compared to the hyperfine structure of the molecule. [1] M. V. Berry, F.R.S., Proc. R. Soc. Lond. A., {\bf 382}, 45 (1984). [Preview Abstract] |
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D1.00048: Dissociative Fragmentation of Polyciclic Aromatic Hydrocarbons with 532 nm Laser Radiation Carmen Cisneros, Juan Carlos Poveda, Manuel Combes, Alfonso Guerrero, Ignacio Alvarez A pulsed supersonic jet of polyaromatic hydrocarbons mixed with
noble gases
was produced by adiabatic expansion in a high vacuum chamber
(2x10$^{-8}$
torr). The PAH's were heated in order to obtain their vapors. The
pulsed
mixtures interacted at 90\r{ } degrees with the 532 nm laser
radiation from
second harmonic of a Nd:YAG laser at intensities of
10$^{11}$-10$^{12}$
W$\cdot $cm$^{-2}$. The produced ions from
photodissociation-photoionization
processes were extracted, accelerated at 3.5 keV and analyzed in
a time of
flight mass spectrometer. In previous work (1) with 355 nm, only
low mass
ions were detected. At the present wave length, single charged
ions were
observed with compositional arrangements of the type
C$_{n}$H$_{m}^{+1}$
with 3$ |
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D1.00049: PHOTON INTERACTIONS WITH ATOMS, IONS, AND MOLECULES; SHORT PULSE PROCESSES |
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D1.00050: Theory of x-ray absorption by laser-dressed atoms Christian Buth, Robin Santra We present an \emph{ab initio} theory for the x-ray photoabsorption cross section of atoms in the field of a moderately intense optical laser ($800 \, \mathrm{nm}$, $10^{13} \, \mathrm{\frac{W}{cm^2}}$). The laser dresses the core-excited atomic states, which introduces a dependence of the cross section on the angle between the polarization vectors of the two linearly polarized radiation sources. The strong interaction due to the laser-dressing is treated by diagonalization of a Floquet-type matrix; the weak coupling between x-rays and the atom is described by non-Hermitian perturbation theory. We apply our theory to study the photoabsorption cross section of neon and krypton atoms near the K~edge. A pronounced modification of the cross section is found in the presence of the optical laser --- \textbf{reference:} arXiv:physics/0611122. [Preview Abstract] |
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D1.00051: Interpretation of black body radiation as a decay process Clarence A. Gall The treatment of black body radiation as a decay process with the wavelength $\left( \lambda \right) $ as the time marker, leads to an apportioning function $\left( D_{\lambda }\right) $ that distributes the total thermodynamic Stefan-Boltzmann emitted intensity $\left( I\right) $ over the entire wavelength range (Clarence A Gall, BAPS, March Meeting 2007, Denver, CO). The resulting distribution function $\left( I_{\lambda }=ID_{\lambda }=\sigma \frac{T^{6}}{b^{2}}\lambda e^{-\frac{T}{b}\lambda }\right) $ gives the Stefan-Boltzmann law on integration over the same interval. Differentiation of $I_{\lambda }$ produces Wien's displacement law as the condition for the wavelength at maximum emitted intensity $\left( \lambda _{m}\right) $. Substitution of $\lambda _{m}$ in $I_{\lambda }$ yields the maximum emitted intensity $\left( I_{\lambda _{m}}\right) $ as being proportional to $T\,^{5}$. \ Hence $\ I_{\lambda }$ satisfies exactly the three known empirical laws of black body radiation and fulfils Einstein's hope for a solution of the radiation problem without the use of light quanta. Finally the replacement of $\frac{T}{b}$ \ with a single constant $G$ \ simplifies the distribution function so that \ $I_{\lambda }=\sigma _{G}G^{6}\lambda e^{-G\lambda }$ \ where \ $\sigma _{G}=b^{4}\sigma $. Consequently $\ G$ \ defines a new temperature scale with units of reciprocal wavelength that unifies the thermodynamic and colour scales. [Preview Abstract] |
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D1.00052: Partial and Complete Transfer of Energy in Bremsstrahlung Must Include Spin and Vibrational Kinetic Energies Stewart Brekke When complete braking is achieved, the spin and vibrational kinetic energies as well as linear kinetic energy is transferred to the resulting photon: $h\nu = 1/2mv^2 + 1/2I\omega_r^2 + (n +1/2)\hbar\omega_v$ If partial transfer of kinetic energy is achieved by decelerating a charged particle, then the resulting photon is $[1/2mv^2_2 +1/2I\omega_{r2}^2 + (n+1/2)\hbar\omega_{v2}]- [1/2mv_{1}^2 +1/2I\omega_{r1}^2 + (n+1)\hbar\omega_{v1}]$. $1/2I\omega_r^2$ is the spin kinetic energy and $(n +1/2)\hbar\omega_v$ is the vibrational kinetic energy. By using the spin and vibrational factors some reconciliation of experimental and theoretical values can be achieved. [Preview Abstract] |
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D1.00053: Compton Effect and Pair Production and Annihiliation Formulas Should Include Spin and Vibrational Energy Factors Stewart Brekke The correct formula for the Compton Effect should spin and vibrational energies before and after the photon collision: $hf_1 +mc^2 + 1/2I\omega_{1r}^2 +(n +1/2)\hbar\omega_{1v} = hf_2 +{(p_ec)^2+(mc^2)^2}^{1/2} +1/2I\omega_{2r}^2 +(n+1/2)\hbar\omega_{2v}$. The pair annilhilation formula should be $2hf = m_+c^2 +m_-c^2 +1/2I\omega_{+r}^2 + (n +1/2)\hbar\omega_{+v} +1/2I\omega_{-r}^2 + (n +1/2)\hbar\omega_{-v})$. In pair creation the photon energy must also go to the vibrational and spin kinetic energies besides linear kinetic energies of the created particles. By using the vibrational and and spin kinetic energies some reconciliation between theoretical and experimental values may be achieved. [Preview Abstract] |
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D1.00054: Systematic study of zeros in bound-free matrix elements L.A. LaJohn, R.H. Pratt, S.T. Manson We extend the systematic study of the positions in photon energy at which radial matrix elements are zero, well known for dipole matrix elements, to quadrupole matrix elements, considering the full range of the periodic table. For nonrelativistic dipole matrix elements there are zeros (Cooper minima)(CM) only for screened (not pure point Coulomb) potentials, at energies of a few of tens of eV. There are relativistic zeros (RC) that are independent of potential at much higher energies, around 100 keV or higher. For the case of quadrupole matrix elements, CM and RC zeros are again found in certain channels, but there is also a third class of zeros in an intermediate energy regime (order of 10 keV), already present in the point Coulomb potential (NRC), but modified by screening. These quadrupole zeros have important consequences, particularly for photoelectron amgular distributions. Zeros occur in sequences, of one type for CM and NRC, and of another for RC. [Preview Abstract] |
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D1.00055: Searching for exotic particle emission in the decay of trapped Rb isomers T. Kong, R. Pitcairn, A. Gorelov, J. Fung, C. H\"ohr, M. Pearson, J. Behr During the decay of nuclear isomers, the momentum of the recoil nucleus will change if any massive particle is emitted instead of a Gamma ray. The Rb isomer transitions are sensitive to a mass range between 20 to 550 keV/c$^{2}$. This range covers masses for pseudoscalar axions which were proposed to solve the ``strong CP'' problem and for scalar particles. In our experiment, trapped metastable Rb isomers will be used to search for these particles. To measure the recoiling momentum, the daughter Rb atoms are photo-ionized. The resulting electrons and photo-ions are detected in a MOTRIMS setup, where charged particles are guided onto time and position sensitive detectors by means of electric fields. The photo-ionization involves firstly the excitation from 5S state to 5D state by Doppler-free two-photon transition using an MBR-110 laser at 778nm, and then ionization to the continuum by a broadband diode laser bar. [Preview Abstract] |
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D1.00056: Absorption measurements of alkali-metal resonance lines broadened by He and molecular hydrogen collisions F. Shindo, J. Babb, K. Kirby The optical and near-infrared spectroscopic observations of cool brown dwarfs exhibit very prominent signatures of sodium and potassium resonance lines. The atmospheres of these objects are mainly composed of molecular hydrogen and helium and the collisions of these species with the alkali-metal atoms induce broadening of the K and Na resonance lines by as much as 100 nm either side of the line core. Particularly important are the far line wings, where satellite features which are usually very temperature-sensitive may appear due to extrema in the difference potentials. These features are highly sensitive to pressure and temperature, whereas their position and shape depend critically on the details in the interaction potentials. Accurate line profiles can serve as valuable diagnostics of the physical characteristics of brown dwarfs and extrasolar giant planets. Experimental determinations of the far wings are indispensable in validating the theoretical models. We report here our measurements of the absorption coefficients for pressure broadening in the far wings of the 4s-4p and 4s-5p doublet lines of potassium atoms in the presence of helium and hydrogen gas at temperatures around 900 K. Supported in part by NASA grant NNG06GF06G. [Preview Abstract] |
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D1.00057: Determining accurate laser intensity dependence despite the intensity-volume effect with z-scanning intensity-difference spectra A. Max Sayler, Pengqian Wang, Nora G. Johnson, Biswanath Gaire, Kevin D. Carnes, Itzik Ben-Itzhak A focal spot or z-scanning intensity-difference spectrum method is developed to allow the determination of the intensity dependence of laser-produced features while improving experimental statistics. This method is applicable to a focused Gaussian beam interacting with an approximately uniform planar target. We apply this method to the angularly resolved kinetic energy release spectra of laser-induced dissociation of O$_{2}^{+}$ and H$_{2}^{+}$ so as to keep the exact contribution from a predetermined intensity range and eliminate the contributions from outside this range. [Preview Abstract] |
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D1.00058: Phase noise to intensity noise conversion in EIT Yanhong Xiao, Tun Wang, Michael Hohensee, Irina Novikova, David Phillips, Susanne Yelin, Ronald Walsworth Laser phase noise can induce intensity noise after interacting with an atomic medium. This process plays a critical role in determining the performance of systems employing electromagnetically induced transparency (EIT), including certain types of atomic clocks. We present an experimental and theoretical study of EIT noise spectra and correlations in a Rb vapor cell. Variations of noise features with laser frequency and two-photon detunings are studied systematically with particular emphasis on noise correlations between the two output fields. [Preview Abstract] |
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D1.00059: Photoionization and electron-impact ionization of Ar$^{5+}$ Jing Cheng Wang, M. Lu, D. Esteves, M. Habibi, G. Alna'Washi, R.A. Phaneuf, A.L.D. Kilcoyne, B.M. McLaughlin Absolute cross sections for photoionization and electron-impact ionization of Ar$^{5+}$ have been measured using two different interacting-beams setups. In the energy range from 90 to 111 eV, both electron-impact ionization and photoionization of Ar$^{5+}$ are dominated by indirect $3s$ subshell excitation-autoionization. From 270 to 285 eV, resonances due to $2p-3d$ excitation-autoionization are prominent in the photoionization spectrum. An enhancement due to \textit{2p-nl} (n$>$2) excitations is evident in the electron-impact ionization cross section between 225 and 335 eV. The electron and photon impact data show features due to excitation of the same autoionizing states. The photoionization measurements will be compared to Breit-Pauli R-Matrix calculations. [Preview Abstract] |
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D1.00060: The Iron Project and the RMAX Project: Transitions in Fe~XV, Fe~XVI, and Astrophysical Applications Maximiliano Montenegro, Sultana Nahar, Anil Pradhan, Chiranjib Sur, Justin Oelgoetz While the Iron Project is involved in scattering and radiative atomic processes of iron and iron-peak elements, the Rmax Project aims at the X-ray spectroscopy of astrophysical objects. Under the Iron Project, the oscillator strengths and radiative decay rates for fine structure transitions going up to n=10 and l=9 are obtained for magenesium like Fe~XV and sodium like Fe~XVI. They correspond to 98 levels for Fe~XVI and 504 levels for Fe~XV. We have employed relativistic Breit-Pauli R-matrix method for the allowed electric dipole (E1) transitions and Breit-Pauli atomic structure calculations for forbidden (E2, E3, M1, M2) transitions for these ions. The results have been benchmarked against the ab initio coupled cluster method which includes relativistic effects. Very good agreement is found for Fe~XVI. The application of the Iron Project and the RmaX Project data to laboratory and astrophysical sources is demonstrated for time-resolved spectroscopy of X-ray lines of He-like Fe and Ni, especially for the astrophysical diagnostic lines. [Preview Abstract] |
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D1.00061: $\textit{Ab Initio}$ Theoretical Investigation of the Frequency Comb Structure in the XUV Regime via High Harmonic Generation Juan J. Carrera, Sang-Kil Son, Shih-I. Chu We present an $\textit{ab initio}$ quantum investigation of the frequency comb structure formed within each high harmonic generation (HHG) power spectrum driven by a train of equal- spacing short laser pulses. The HHG power spectrum of atomic hydrogen is calculated by solving the time-dependent Schr\"{o} dinger equation accurately and efficiently by means of the time- dependent generalized pseudospectral method. We found that the frequency comb structure is preserved within each harmonic. In addition, the repetition frequency of the comb laser depends upon the pulse separation $\tau$ and the spectral width of each individual comb fringe is inversely proportional to the number of pulses $(n)$ used. However, the global HHG power spectrum pattern depends only upon the laser frequency and intensity used and is not sensitive to the $\tau$ and $n$ parameters. Finally, the frequency comb structure persists even in the presence of appreciable ionization. [Preview Abstract] |
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D1.00062: A general approach to few-cycle laser interactions with complex atoms Xiaoxu Guan, Oleg Zatsarinny, Klaus Bartschat, Johannes Feist, Barry Schneider, Cliff Noble We are developing a general method to solve the time-dependent Schr\"odinger equation for the interaction of a strong laser pulse with a general atom, i.e., beyond the models of quasi-one or quasi-two-electron targets. The field-free hamiltonian matrices are generated in a $B$-spline $R$-matrix method~[1], and the laser field is coupled in through dipole matrices generated with the same program. The major advantages of our approach are i)~its generality and ii)~the possibility of generating highly accurate target descriptions with small configuration interaction expansions. We propagate the solution of the TDSE by the Arnoldi method~[2]. The generalized eigenvalue problem is transformed by diagonalizing the overlap matrix~$S$ of the non-orthogonal basis functions and generating new field-free hamiltonian and dipole matrix blocks through $ H' = S^{-1/2} H S^{-1/2}$ and $D' = S^{-1/2} DS^{-1/2}.$ Details of various numerical implementations will be discussed. \par\vspace{0.1truecm}\noindent [1] O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). \par\noindent [2] T.J.~Park and J.C.~Light, J. Chem. Phys. {\bf 85}, 5870 (1986). [Preview Abstract] |
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D1.00063: Creating and manipulating vibrational wavepackets of the D$_{2}^{+}$ molecular ion. Jarlath McKenna, Chris Calvert, Domhnall Murphy, Jim McCann, Ian Williams, William Bryan, Elizabeth English, Joseph Wood, Roy Newell, Edmond Turcu The creation of a vibrational wavepacket within a molecular system shows great promise as an active method of both tracking and controlling nuclear motion on femtosecond timescales. However the coherent excitation of the vibrational eigenstates of the molecule, and the subsequent imaging of the bond vibration, requires pulse durations on the order of the vibrational period. For the theoretically tractable hydrogen molecular ions, such timescales are on the order of 20 fs or less. As such, intense few-cycle infrared laser pulses are required. We present here a study where we excite and subsequently map out the quantum revival of a vibrational wavepacket of D$_{2}^{+}$, tracking the nuclear motion over hundreds of femtoseconds. By rigorous modeling of the nuclear motion the experimental results are reproduced to high agreement, and new methods to control both molecular dissociation and vibrational state population are proposed. [Preview Abstract] |
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D1.00064: Wave packet dynamics in doubly excited states of He Johannes Feist, Stefan Nagele, Emil Persson, Joachim Burgd\"orfer, Barry Schneider We have developed a method for the ab initio simulation of the interaction of ultrashort laser pulses with helium atoms. We expand the two-electron Schr\"odinger equation in coupled spherical harmonics and perform direct time integration utilizing either the Arnoldi-Lanczos or the Leapfrog method. The spatial discretization is performed in an FEDVR basis~[1]. This allows for a numerically accurate description while possessing desirable computational features, e.g. a block-diagonal form of the kinetic energy matrix. We will present results on electron-electron correlation and wave packet dynamics in He. By using a suitable combination of attosecond XUV/EUV pulses, we prepare a wave packet in the doubly excited states of helium. The motion of this wave packet can be observed by using a probe pulse to induce ionization. We aim for a detailed understanding of the process by a careful study of the ionized electrons, e.g. by investigating doubly differential momentum spectra. \renewcommand{\labelenumi}{[\arabic{enumi}]}\begin{enumerate} \item B.~I. Schneider and L.~A. Collins. \emph{J. Non-Cryst. Solids} \textbf{351}, 1551. \end{enumerate} [Preview Abstract] |
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D1.00065: The dynamics of meta-stable states described with a complex scaled Hamiltonian Eva Lindroth, Jakob Bengtsson, S{\o}lve Selst{\o} The laser development has given access to light pulses in the femto- and subfemtosecond regime and thereby opened the possibility to follow electron dynamics directly in the time domain. Of special interest is the dynamics of {\it resonant states}, and pioneering experimental studies were made a few years ago on the Auger decay of inner-shell vacancies. We present a new method for time-dependent calculations of the whole sequence of events when an atom is exposed to a short light pulse followed by the population of a meta-stable state, and with the possibility to follow its subsequent decay by electron ejection. We use the method of complex scaling and show how it can be used together with the time-dependent Schr\"{o}dinger equation. Important advantages with this approach are; the meta-stable states are obtained as unique eigenstates to the field-free complex scaled Hamiltonian and the continuum is adequately represented by a very modest number of eigenstates. We have tested our approach against conventional methods for hydrogen and established the connection to Floquet theory for monochromatic radiation. [Preview Abstract] |
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D1.00066: Strong-Field Double Ionization of H$_{2}$/D$_{2}$ : Wavelength Dependent Study Igor Litvinyuk, Ali Alnaser, Daniel Comtois, Asad Hasan, David Villeneuve, Jean-Claude Kieffer We studied double-ionization of H$_{2}$ and D$_{2}$ by intense femtosecond laser pulses of different wavelengths (500, 600, 800, 1300, 2000 nm) and peak intensities. The kinetic energy release (KER) spectra measured in the Coulomb explosion of the molecules were used to identify the various mechanisms responsible for the dissociation and ionization of H$_{2}$/D$_{2}$ in the laser fields. In addition to fragments from well known bond softening and enhanced ionization channels, high energy protons/deuterons of KER around 11 eV were for the first time observed when using short wavelengths (500 and 600 nm) at high-peak intensities. This channel exhibited wavelength dependence, with KER decreasing for longer wavelengths. This observation implies that a multiphoton-ionization process is actively operating at short internuclear distances and must be accounted for to correctly understand the strong-field ionization of H$_{2}$/D$_{2}$ by short laser pulses. [Preview Abstract] |
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D1.00067: Study of D$_{2}$ and H$_{2}$ nuclear dynamics in strong laser field using Coulomb Explosion Imaging Irina Bocharova, Igor Litvinyuk, Lewis Cocke, Dipanwita Ray, Chakra Maharjan, Predrag Ranitovic For small molecules like H$_{2}$ and D$_{2}$ most of the nuclear wavepacket motion is expected to occur on femtosecond time scale. To probe such a fast dynamics Coulomb explosion imaging is used in combination with short (8 fs) pulses and pump-probe technique. We use COLTRIMS technique to collect fragments of Coulomb explosion of molecules in coincidence and calculate kinetic energy release of these fragments as well as molecular orientation before the explosion as a function of time. It allows us to track vibration and rotational nuclear wavepackets and follow the dissociation process of hydrogen and deuterium molecules. [Preview Abstract] |
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D1.00068: Holographic Generation and 3-D Ion Imaging of Focused Ultrashort Pulses of Complex Light James Strohaber, Chad Petersen, Cornelis Uiterwaal We investigate an open question in intense-field physics: are excitation and ionization with ultrashort pulses affected by optical orbital angular momentum (OAM)? To answer this question, we holographically create Laguerre-Gaussian paraxial modes, which carry optical OAM. In our experiments we use a computer-controlled spatial light modulator to modulate the transversal profile of 50-fs, 800-nm pulses. Using phase-only masks that also encode the amplitude profile of the desired mode we create $\mu $m-sized foci of complex light. We analyze the mode purity of our foci on-site by imaging them with ions, which act as local intensity sensors. We obtain three-dimensional images of the foci without requiring assumptions about their geometry. We also use ion imaging to realize a photo-dynamical test tube, by recording ions created in the `hottest' spot of the focus only, with unsurpassed $\mu $m resolution. This allows us to study ionization processes without having to integrate yields over the whole focal region. Finally, we also present a new set of steady-state modes in quadratic lenslike media; these modes are separable solutions in cylindrical parabolic coordinates. Recent progress will be discussed. [Preview Abstract] |
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D1.00069: Ionization of N$_{2}^{+}$ and O$_{2}^{+}$ beams in femtosecond intense laser fields. A.M. Sayler, B. Gaire, Nora G. Johnson, M. Leonard, E. Parke, K.D. Carnes, I. Ben-Itzhak, P.Q. Wang The dissociative ionization of N$_{2}^{+}$ and O$_{2}^{+}$ molecular ion beams has been studied using laser pulses of 790 nm, 10-45 fs and up to 2$\times $10$^{15}$ W/cm$^{2}$. The momentum distributions of the dissociation channels N$^{+ }$+ N$^{+}$ and O$^{+ }$+ O$^{+}$ are measured by a three-dimensional momentum imaging method. The angular distributions of the ionization of these two molecules exhibit significant differences, which will be compared to theoretical predictions. The angular distribution of the ionization of O$_{2}^{+}$ is found to strongly depend on the kinetic energy release. The branching ratios and the intensity dependence of the ionization channels will also be discussed. [Preview Abstract] |
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D1.00070: Double- Ionization of Ar and Ne in Colors Ali S. Alnaser, D. Comtois, A.T. Hasan, D.M. Villeneuve, J.-C. Kieffer, I.V. Litvinyuk We have conducted a systematic study on the double ionization of Ar and Ne atoms to investigate the origin of the dip in the longitudinal momentum distribution of the doubly-charged recoil ions. We used a wide range of wavelengths (483, 800, 1313, 2016 nm) and laser peak intensities. The momentum distributions of the doubly-charged recoil ions in the direction parallel to the laser polarization were measured with sufficiently high resolution. At 800 nm, Ne$^{2+}$ exhibits a pronounced dip around zero momentum, while Ar$^{2+}$ shows a shallow one. When using the longer wavelengths (1313 and 2016 nm) the dip in the momentum distribution of both ions becomes very distinct, while with the shorter wavelengths the dip gets much shallower in Ne$^{2+}$ and almost disappears in Ar$^{2+}$. Our results indicated that the origin of the dip is \textit{principally} due to the interplay between the maximum energy gained by the rescattering electron in the laser field and the ionization potential of singly- charged ion. [Preview Abstract] |
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D1.00071: Extremely short pulses in Maxwell-Duffing model Utpal Roy, Prasanta K. Panigrahi We analyze the reduced Maxwell-Duffing model relevant for ultra short pulse propagation in non-resonant media. We find a wide class of localized pulse solution, through a novel method. It is observed that, these solutions are related to non-linear Schr\"{o}dinger equation with a source. We also find continuous wave solutions. Some of the solutions are singular, indicating self-focusing effect. Modulation instability and stability analysis of the solutions have also been studied. [Preview Abstract] |
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D1.00072: Time-dependent dynamics of intense laser-induced above threshold Coulomb explosion B.D. Esry, I. Ben-Itzhak We use our recently proposed model [1] to extract information about the nuclear dynamics from the recent Coulomb explosion data of Staudte {\it et al.} taken with 40 fs pulses [2]. That data, taken at multiple intensities near the ionization appearance intensity for both H$_2$ and D$_2$ in linearly and circularly polarized light, shows remarkable structure and regularity not easily explained by conventional models. Because our model does fit the spectra well, we can infer the qualitative time-dependent evolution of the system. In addition, we speculate about the possibility of rescattering leading to above threshold Coulomb explosion. \smallskip \newline [1] B.D. Esry, A.M. Sayler, P.Q. Wang, K.D. Carnes, and I. Ben-Itzhak, Phys. Rev. Lett. {\bf 97}, 013003 (2006). \newline [2] A. Staudte, D. Pavici\'c, S. Chelkowski, D. Zeidler, M. Meckel, H. Niikura, M. Sch\"offler, S. Sch\"ossler, B. Ulrich, P. P. Rajeev, Th. Weber, T. Jahnke, D.M. Villeneuve, A.D. Bandrauk, C.L. Cocke, P.B. Corkum, and R. D\"orner, Phys. Rev. Lett. (accepted). [Preview Abstract] |
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D1.00073: Progress report on the applications of an ultrafast electron source Shawn Hilbert, Brett Barwick, Adam Caprez, Cornerlis Uiterwaal, Herman Batelaan Femtosecond laser pulses are used to create ultrafast electron pulses from a tungsten nanometer field emission tip. The emission process is rich in features and allows the study of thermionic emission, multi-photon over-barrier emission, ATI-emission, and field induced tunneling [1]. Evidence for the first three processes are presented. The application of the source for interaction between free electrons and laser light [2], and its relation to dispersion compensation for electron wave packets will be discussed. The use of the source to study low energy with high resolution electron physics is presented. The application of the source to investigate the macroscopic limit of the Aharonov-Bohm effect is tested. And finally, attempts to observe diffraction-in-time as a means to probe attosecond physics are reported. [1] Peter Hommelhoff, et al. Phys. Rev. Lett. \textbf{97}, 247402 (2006), [2] Kapitza-Dirac diffraction without standing waves: diffraction without a grating? O. Smirnova, D. L. Freimund, H. Batelaan\textbf{, }M. Ivanov, Phys. Rev. Lett. \textbf{92}, 223601/1 (2004). [Preview Abstract] |
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D1.00074: Fragmentation of H$_{2}^{+}$ molecules irradiated by intense 395 nm femtosecond laser pulses: a coincidence 3D momentum imaging study. Jarlath McKenna, A. Max Sayler, P.Q. Wang, Bishwanath Gaire, Nora G. Johnson, Eli Parke, F. Anis, Jianjun Hua, B.D. Esry, Kevin D. Carnes, Itzik Ben-Itzhak As the most fundamental molecule, H$_{2}^{+}$ is the natural choice of study to understand fast molecular response to intense ($>$ 10$^{12}$ W cm$^{-2})$ short pulse ($<$ 100 fs) laser fields. Previously this molecular ion, prepared as a fast ($\sim $10 keV) target, has been explored by our group using a 790 nm Ti:Sapphire laser revealing, for example, interesting structure in the ionization channel attributed to above-threshold Coulomb explosion. Using the second harmonic of this frequency (395 nm light) provides better energy resolution of photon-order dependent processes. As such we present here a coincidence 3D momentum imaging study of H$_{2}^{+}$ at this wavelength and compare the results to those using 790 nm light centering the discussion on both the ionization and dissociation channels. A theoretical interpretation of the results is offered. [Preview Abstract] |
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D1.00075: Quantitative comparison between theory and experiment for dissociation of H$_{2}^+$ in ultrashort laser pulses Fatima Anis, Pengqian Wang, A. Max Sayler, Bishwanath Gaire, Nora Johnson, Eli Parke, Jarlath Mckenna, Kevin Carnes, Itzik Ben-Itzhak, Brett Esry We have performed calculations for H$_{2}^+$ dissociation in an intense laser pulse including all possible physical processes except ionization. In particular, we have included nuclear vibration and rotation as well as electronic excitation. We compare these results to data we have obtained from kinematically complete measurements, including both the ionic H$^+$ and neutral H fragments dissociated from an H$_{2}^+$ beam, achieved through coincidence three-dimensional momentum imaging. To make the comparison as quantitative as possible, we have averaged the theoretical results over Frank-Condon, intensity, and rotational distributions to best match the experimental conditions. Rotational motion in H$_{2}^+$ is found to be important even for ultrashort pulses ranging from 10-45fs FWHM. [Preview Abstract] |
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D1.00076: Numerical explorations of above threshold Coulomb explosion for H2+ in an intense laser pulse Jianjun Hua, Brett Esry Above threshold Coulomb explosion is a mechanism recently invoked by Esry et al. [1] to explain previously unobserved structure in the kinetic energy release (KER) spectrum of intense laser induced ionization of H2+. Based on a diabatic Floquet-Born-Oppenheimer picture, above threshold Coulomb explosion predicts multiple sequences of peaks separated by a photon's energy. This model was able to fit the experimental KER data in [1] quite well and allowed predictions about the angular distribution that were also verified in [1]. Nevertheless, fundamental questions about the model remain that we will try to address by solving the time-dependent Schroedinger equation. For simplicity, we solve a one-dimensional model for H2+ that should retain the physics of above threshold Coulomb explosion. We will discuss the results of this numerical test. \newline [1] B.D.Esry, A.M.Sayler.,P.Q.Wang,K.D.Carnes,and I.Ben-Itzhak, Phys. Rev. Lett. 97,013003(2006) [Preview Abstract] |
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D1.00077: RYDBERG AND EXOTIC ATOMS AND MOLECULES |
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D1.00078: A wavelet based time-frequency analysis of wave packet fractional revivals Suranjana Ghosh, Jagannath Banerji We show that the time-frequency analysis of the autocorrelation function based on its wavelet transform [1], is a better tool to resolve fractional revivals [2] of a wave packet than the usual time domain analysis. We study the above for two different systems like a Rydberg atom [3] and a diatomic molecular system [4] and show that the present method can resolve fractional revivals of higher order than what can be achieved by the time domain analysis. This advantage is crucial in reconstructing the initial state of the wave packet when its coherent structure is short-lived and decays before it is fully revived. References: [1] R. M. Rao and A. S. Bopardikar, \textit{Wavelet Transforms: Introduction to Theory and Applications }(ADDISON-WESLEY, 2000). [2] I. Sh. Averbukh and N. F. Perelman, Phys. Lett. A 139, 449 (1989); R. W. Robinett, Phys. Rep. 392, 1 (2004) and references therein; J. Banerji and S. Ghosh, J. Phys. B 39, 1113 (2006). [3] Z. D. Gaeta and C. R. Stroud, Jr., Phys. Rev. A 42, 6308 (1990). [4] S. Ghosh, A. Chiruvelli, J. Banerji and P. K. Panigrahi, Phys. Rev. A 70, 053813 (2006). [Preview Abstract] |
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D1.00079: Electric Dipole Echoes in Rydberg Atoms Shuhei Yoshida, Carlos Reinhold, Joachim Burgdorfer, Wei Zhao, Jeffrey Mestayer, Jim Lancaster, F. Barry Dunning We report the first observation of echoes in the electric dipole moment of an ensemble of Rydberg atoms precessing in an external electric field $F$. Quasi-one-dimensional Rydberg atoms oriented along the $x$ axis are first produced and then subjected to a dc field $F$ = 20mVcm$^{-1 }$that is suddenly applied in the $z$ direction to create a Stark wavepacket whose evolution is monitored using a half-cycle probe pulse. The wavepacket contains states of different n that precess at different rates leading to dephasing. Rapid reversal of the field $F \to -F$ at t = $\tau $ is shown to play the role akin to that of a $\pi $-pulse in NMR in rephasing the dephased ensemble resulting in the build-up of an echo at t $\sim $ 2$\tau $. The appearance of the echo is explained with the aid of classical trajectory Monte Carlo simulations. [Preview Abstract] |
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D1.00080: Ionizing Kicked Hydrogen with Homoclinic Tangles Korana Burke, Kevin Mitchell A kicked hydrogen atom subjected to alternating periodic forcing by an external electric field exhibits chaotic behavior. We study the geometry of homoclinic tangles that arise in phase space and use the knowledge we gain from the transport of the charged particle through a ``turnstile'' to draw conclusions about the ionization rate. We apply both delta function and square-shaped alternating kicks to the charged particle. In order to study the escape rate we form the initial conditions by populating an energy eigenstate or a minimum uncertainty wavepacket. We examine the lobe dynamics and give conclusions about how the size and shape of the lobes influence the phase space transport. The classical calculations can be applied to the study of ionization rates of highly excited Rydberg atoms. [Preview Abstract] |
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D1.00081: A study of adiabatic population transfer for the production of heavy Rydberg systems Jeffrey Philippson, Ralph Shiell We present recent progress towards the production of heavy Rydberg systems within alkali metal dimers using STIRAP to effect vibrational state transfer followed by excitation with a pulsed UV laser. We have calculated the efficiency of adiabatic population transfer in a 2-level system and investigated its dependence on the temporal profile of the perturbation. We show that the optimal profile for adiabatic following results in a significantly lower probability of a non-adiabatic transition than that predicted by applying the Landau-Zener formula. We have also determined the relationship between population-loss and beam profile for a 3-level system undergoing a STIRAP process. These theoretical predictions will be compared with results from a molecular beam experiment within which lithium dimers cross beams from a pair of diode lasers tuned to the $A ^1\Sigma_u^+$ - $X ^1\Sigma_g^+$ transition. [Preview Abstract] |
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D1.00082: Non-Degenerate Four-Wave Mixing through Rydberg States in a MOT Jason Day, Erik Brekke, Thad Walker In this work, we use a three-photon near-resonant process in a laser-cooled Rb vapor to achieve phase-matched four-wave mixing using an intermediate Rydberg state. Rydberg atoms in the 36D5/2 state are efficiently produced using a 780 nm/480 nm two-photon excitation detuned 500 MHz above the 5P3/2 intermediate state. When a 1019 nm laser stimulates emission down to the 6P3/2 state, the Rydberg atom populations are significantly depleted and 422 nm 6P3/2-5S photons are observed by photon-counting photomultiplier tubes. With the 780 nm, 480 nm, and 1019 nm lasers configured in a non-collinear phase-matched geometry, we observe a coherent 422 nm phase-matched signal that is up to 10 times larger than the non-phase-matched radiation. Under these phase-matched conditions, the incoherent radiation is partially depleted. These experiments demonstrate the ability to coherently manipulate ultracold atoms at optical frequencies using Rydberg states. [Preview Abstract] |
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D1.00083: Rydberg Ion Fine Structure Measurements with the RESIS Method C.W. Fehrenbach, S.R. Lundeen Measurements of Rydberg fine structure provide precise determinations of positive ion properties such as polarizabilities and permanent moments. The Resonant Excitation Stark Ionization Spectroscopy (RESIS) method, which has provided a range of such measurements in neutral atoms and molecules [1], has recently been extended to study of Rydberg ion fine structure. In principal, the method can be applied to study positive ions of arbitrary charge. The factors limiting signal to noise and frequency resolution in measurements of this type will be discussed, and some possible future applications will be described. [1] S.R. Lundeen in \textit{Advances in Atomic, Molecular, and Optical Physics}, edited by Chun C. Lin and Paul Berman (Academic Press, 2005), Vol 52, pp. 161-208 [Preview Abstract] |
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D1.00084: Rydberg tagging time-of-flight imaging to study ultracold collisions Jonathan Tallant, K. Richard Overstreet, Arne Schwettmann, James P. Shaffer We have further developed Rydberg tagging time-of-flight and imaging techniques so that they can effectively be used to study ultracold collisions. We have realized a velocity resolution of $\sim2.5$ cm/s with our apparatus. This resolution enables Rydberg tagging time-of-flight and imaging spectroscopy to determine the exit channel of an ultracold collision. Results and prospects for applying these methods to measure differential cross-sections for Rydberg atom collisions, photoassociative collisions, and three-body recombination will be presented. [Preview Abstract] |
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D1.00085: Efficient broadband de-excitation of Rydberg atoms with half-cycle pulses Kourosh Afrousheh, Andrew Speck We report on progress towards demonstrating population redistribution of Rydberg atoms using a train of unipolar terahertz bandwidth pulses (half-cycle pulses) as initially proposed by Hu and Collins [1]. In principle this broadband technique should allow the efficient de-excitation of antihydrogen atoms from the currently produced mix of excited states to the ground state which is a necessary prerequisite for a CPT comparison with hydrogen. Here a cloud of ultracold $^{85}\mathrm{Rb}$ atoms are excited to a Rydberg state with $n\approx 40$, allowed to interact with an 80 MHz pulse train of half-cycle pulses, and then the final state distribution is measured. Initial demonstrations of the techniques used for the generation of half-cycle pulses and Rydberg atom production will be described. \newline [1] S. X. Hu and L. A. Collins, Phys. Rev. A 69, 041402 (2004). [Preview Abstract] |
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D1.00086: Angular Studies of Xenon Rydberg Atom Ionization at Au(111) Surfaces H.R. Dunham, D.D. Neufeld, J.C. Lancaster, S. Wethekam, F.B. Dunning The ionization of xenon atoms excited to the lowest states in the $n = 17$ and $n = 20$ Stark manifolds at a flat Au(111) surface is being examined over a range of incident angles. The data suggest that, despite the strong perturbations in the energies and structure of the atomic states that occur as the surface is approached, the experimental data can be well fit by assuming that the ionization rate on average increases exponentially as the surface is approached. Under appropriate conditions, each incident atom can be detected as an ion and the inferred mean ionization distances are in reasonable agreement with theoretical predictions. [Preview Abstract] |
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D1.00087: Ionization of xenon Rydberg atoms at oxidized Si(100) surfaces Dennis Neufeld, Hardin Dunham, Jim Lancaster, Barry Dunning, Stephan Wethekam The ionization of xenon Ryberg atoms incident at near grazing angles on an oxidized Si(100) surface is being examined. Comparison to earlier measurements at a Au(111) surface suggests that ionization, i.e., electron tunneling, occurs much further from the surface and at atom-surface separations that are physically unreasonable. A number of possible explanations for these observations have been considered including both ion reflection and the presence of stray electric fields at the surface. Model calculations suggest that even relatively small variations in surface potential due, for example, to surface charging can lead to the generation of strong local fields sufficient to field ionize the incident atoms before tunneling occurs. This effect is discussed together with possible applications in the detection of low-n Rydberg atoms. [Preview Abstract] |
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D1.00088: Resonance states with unnatural parity in the (e$^{+}$-He$^{+}$) system Z.-C. Yan, Y.K. Ho Bhatia and Drachman reported two S-wave resonances in positron scattering by a helium ion (He$^{+})$ [1]. Since then, there has been considerable interest in the investigation of the resonances for this system [2]. In these works resonances with natural parity were investigated. In the present work, we apply the$^{ }$method of complex-coordinate rotation to investigate resonances with unnatural parity in the positron-helium-ion system. We have calculated some $P^{e, }D^{o}, F^{e}, G^{o}, $and $H^{e}$ resonance states using highly correlated Hylleraas-type wave functions [3]. While such resonances cannot be reached by positron collision with the ground state helium ion, they can be reached, in principle, by positron scattering with the helium ion in one of its excited states. [1] A. K. Bhatia and R. J. Drachman, \textit{Phys. Rev. A} \textbf{42}, 5117 (1990). [2] Y. K. Ho, \textit{Phys. Rev. A}\textbf{ 53}, 3165 (1996); Y. K. Ho and Z.-C. Yan, \textit{Phys. Rev. A}\textbf{\textit{ }}\textbf{66}, 062705 (2002); A. Igarashi and I. Shimamura, \textit{Phys. Rev. A} \textbf{70}, 012706 (2004); Nobuhiro Yamanaka \textit{et al}, Phys. Rev. A\textbf{ 70}, $062701$ (2004). [3] Z.-C. Yan and G. W. F. Drake, \textit{Chem. Phys. Lett.} \textbf{259}, 96 (1996). [Preview Abstract] |
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D1.00089: Diode pumped continuous wave Cs vapor laser with 10W output Randall Knize, Boris Zhdanov We have demonstrated an efficient Cesium vapor laser pumped by a continuous wave narrowband Laser Diode Array (LDA). To obtain a high efficiency, it is necessary to narrow the linewidth of the LDA pump radiation to match the Cs atom absorption line. At a buffer gas pressure close to 1 atm the Cs absorption linewidth is about 15 GHz, which is much less than typical linewidth of commercially available LDAs (about 1 THz). An external cavity with wavelength sensitive narrowband filter was used to narrow an LDA linewidth to below 1 GHz. A heated 2 mm Cs cell with 500 torr ethane was assembled inside a half confocal laser cavity. The spatially multimode pump beam was focused into the cell. The experiment yielded about 10~W output power at 25 W pump power. The Cs vapor laser operated at 894 nm in single longitudinal and fundamental transverse modes. The developed laser can be used for laser cooling experiments. We acknowledge support from NSF, AFOSR and JTO-HEL.. [Preview Abstract] |
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D1.00090: COLLISIONS OF ATOMS WITH ATOMS, ANTIMATTER, MOLECULES, CLUSTERS, AND SURFACES |
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D1.00091: Method to compute wave function evolution from microscopic to macroscopic distances James Sternberg The treatment of loosely bound and continuum electrons in atomic collisions has provided challenges for calculations of these systems. These challenges have not been fully overcome for ion- atom collisions since electron wave functions evolve from microscopic to macroscopic distances. One major source of difficulty is that solutions to the time-dependent Schr\"odinger equation contain an essential singularity at infinity which makes numerical modeling of these systems difficult for large distances. We have identified this essential singularity and developed a method to treat these systems which is extremely efficient and stable. The method is Gallelian invariant, which avoids any ambiguity about what the proper frame of reference should be. It also avoids numerical inaccuracies induced by reflection or absorption at finite boundaries. Wave functions can easily be propagated out to macroscopic distances instead of only approximately 100 au. Finally, the results are consistent with the hidden crossing theory at low impact energies and the Born theory at high energies. In both regimes the electron distribution agree qualitatively with experiment. [Preview Abstract] |
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D1.00092: Resonance structure in the dipositronium molecule Joseph Di Rienzi, Richard Drachman We are investigating the resonances, first reported by Adhikari [1], occurring in the scattering of pairs of positronium atoms. In particular, we are testing the hypothesis that these resonances occur at energies corresponding to ``bound'' states of the positronium ion (either positive or negative) and an electron or positron, respectively. The potential producing the binding is Coulombic at large distances and modified at small distances. Such a model was successful in the analogous case of Ps-H scattering [2], and it would be interesting if it also worked in the present case. A complication in the dipositronium system is that the two positive particles (positrons) are identical, whereas in the Ps-H case the positive particles (positron and proton) are distinct. \newline \newline [1] S. H. Adhikari, Phys. Lett.A \textbf{294, }308 (2002). \newline [2] J. Di Rienzi and R. J. Drachman, Phys. Rev. A \textbf{65}, 032721 (2002); R. J. Drachman, \textit{ibid} \textbf{19}, 1900 (1979). [Preview Abstract] |
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D1.00093: Near Threshold Positron Impact Ionization of Hydrogen Krista Jansen, S.J. Ward, J. Shertzer, J.H. Macek The hyperspherical hidden crossing method is used to calculate the ionization cross section for e$^{+}$-H near threshold. The Wannier ridge for positron impact ionization corresponds to a co-linear arrangement with the electron between the positron and proton and $r_- /r_+ =.4643$. The adiabatic Hamiltonian for total angular momentum zero is expanded about the saddle point and the analytic adiabatic energies are used to obtain the threshold law for breakup: $\sigma (E)\propto E^{2.64}\exp [-0.49\sqrt E ].^{ }$Our results are consistent with the previous values of the Wannier exponent$^{1}$ and the second order correction terms to the threshold law$^{2,3}$. Using our numerical results for the transition probability in the interaction region, we calculated the absolute $S-$wave ionization cross section. $^{1}$H. Klar, J. Phys. B \textbf{14}, 4165 (1981). $^{2}$W. Ihra et al., Phys. Rev. Lett. \textbf{78}, 4027 (1997). $^{3}$J. Sternberg et al., Bull. Am. Phys. Soc. \textbf{49}, 52 (2004). [Preview Abstract] |
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D1.00094: Generalized polarizabilities of Ps negative ion Anand Bhatia, Richard Drachman The positronium negative ion, consisting of two electrons and a positron, is particle stable and decays only by e$^+$ and e$^-$ annihilation into gamma rays. In the past, we have calculated various properties like ground state [$^1S$] energy, decay rate, and photodetachment cross sections. The latter could be used to generate positronium (Ps) beams of controlled energy by accelaration of the Ps negative ion and then photodetaching one of the electrons. A possible type of metastable excited state of the dipositronium molecule (Ps$_2$) has the form of a Ps$^-$ and a positron in a Rydberg state. Although the modified Coulomb potential will account for most of the binding energy, for high $L$ states the generalized polarizabilities [$\alpha_i$, $\beta_i$, $\gamma_i$, i=1,2] will contribute small but significant energy shifts. We calculate these quantities by the pseudostate method. Ps$^-$, being a loosely bound system, has very large polarizabilities as compared to those of the hydrogen ion [H$^-$] and the helium atom. [Preview Abstract] |
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D1.00095: Electron and positron scattering experiments James Sullivan, Adric Jones, Peter Caradonna, Andrew Manning, Terrance Sak, Stephen Buckman The final commissioning of the Australian Positron Beamline Facility is almost complete, and it is anticipated that the first experimental results for positron scattering will be obtained this year. In addition, a novel electron scattering experiment has been constructed making use of the same scattering techniques. While the APBF uses a Surko trap to generate a cold, pulsed positron beam, the new electron scattering experiment makes use of thermionic emission and a pulsed electrode to make a similarly pulsed electron beam. By using a retarding potential difference technique, the energy spread of the electrons is able to be reduced compared to the initial distribution from the filament before being directed to a scattering cell. The scattering and analysis is the same as that for the Surko scheme, but due to the compact nature of the electron source, the experiment is highly compact and correspondingly inexpensive. This poster will present the current state-of-play with the positron scattering program at the ANU, along with a detailed explanation of the construction and operation of a cheap, yet effective, experiment to perform electron scattering measurements. An outline of the proposed experimental program for both apparatus will also be given. [Preview Abstract] |
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D1.00096: Comparisons of Differential Double Ionization of Ar by Positron and Electron Impact O.G. de Lucio, J. Gavin, R.D. DuBois, A.C.F. Santos Differential cross sections for single and multiple ionization of argon by 500 eV positrons and electrons are being measured. The goal of this work is to investigate projectile charge effects in the ionization kinematics. Using coincidences between projectiles which have lost specific amounts of energy and recoil ions, ratios of double to single ionization as a function of energy loss were studied. These data are being used to investigate interference between the TS1 and TS2 terms leading to double ionization. Using coincidences between ejected electrons and recoil ions, angular distributions for electron emission resulting from single and multiple ionization were studied. Ratios of the angular distributions provide insight into the relative importance of the TS1 and TS2 mechanism for double ionization. Initial analysis implies differences for positron and electron impact. [Preview Abstract] |
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D1.00097: A Proposed Apparatus for Efficiently Trapping and Cooling Positrons. Jason Engbrecht, Daniel Endean Previous work has shown the ability to trap positrons efficiently for long periods of times using a Penning trap. Utilizing strategically placed electrostatic wells, axial energy is transferred into cyclotron energy temporarily trapping the positrons. Combined with a ramping potential on one end of the trap, trapping times of a few ms with efficiencies of approximate 20{\%} were achieved to produce a beam with a high energy spread ($\sim $100 eV). We have developed a simulation of this system for the purpose of studying its dynamics. From this simulation we have discovered the role of resonance between the cyclotron orbit and the length of the potential well. We have also examined the potential for a newly optimized trap based on this design that implements gas or electronic cooling to reduce the energy spread of the positrons. [Preview Abstract] |
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D1.00098: Inelastic Transitions in Slow Collisions of Anti-Hydrogen with Hydrogen Atoms Robert Harrison, Predrag Krstic We calculate excited adiabatic states and nonadiabatic coupling matrix elements of a quasimolecular system containing hydrogen and anti-hydrogen atoms, for a range of internuclear distances from 0.2 to 20 Bohrs. High accuracy is achieved by exact diagonalization of the molecular Hamiltionian in a large Gaussian basis. Nonadiabatic dynamics was calculated by solving MOCC equations. Positronium states are included in the consideration. [Preview Abstract] |
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D1.00099: Positron scattering on highly excited antihydrogen atom in strong magnetic field D. Vrinceanu, T. Pohl, H.R. Sadeghpour Classical Trajectory Monte Carlo simulation technique is employed to study the collision of a positron on highly excited antihydrogen atom in conditions similar to Penning trap experiments. The main difficulty is generating a distribution of initial conditions which describes accurately an atom of given energy and angular momentum projection in strong magnetic field. The quality of the non-perturbative ensemble proposed here is verified by calculating, and comparing, various average quantities in both classical and quantum mechanical ways. The results for energy and angular momentum transfer are presented for a wide range of positron projectile energies. [Preview Abstract] |
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D1.00100: Cooling by Spontaneous Decay of Highly Excited Antihydrogen Atoms in Magnetic Traps Thomas Pohl, Hossein R. Sadeghpour, Yugo Nagata, Yasunori Yamazaki An efficient cooling mechanism of magnetically trapped, highly excited antihydrogen atoms is presented. This cooling, in addition to the expected evaporative cooling, results in trapping of a large number of atoms in the ground state, essential for future antihydrogen trapping experiments. In good agreement with our numerical simulations, we identify two different dynamical regimes - adiabatic cooling followed by sudden de-excitation. Moreover we derive expressions for the cooling efficiency, which may help to design trap geometries with optimized groundstate trapping. [Preview Abstract] |
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D1.00101: First principles study of adsorption and dissociation of H$_2$, O$_2$, and CO on Pt$_4$ and Pt$_3$Co clusters T. J. Dhilip Kumar, Chenggang Zhou, Balakrishnan Naduvalath, Robert C. Forrey, Hansong Cheng Pt and Pt based alloy nanoparticles have received much attention recently in designing improved catalysts for the oxygen reduction reaction in fuel cell electrodes. In particular, Pt-Co alloy systems have attracted significant interest in proton exchange membrane fuel cells. To gain physical insight into the catalytic properties of Pt and Pt-Co alloys we have performed fundamental studies on Pt$_4$ and Pt$_3$Co alloy clusters using first principles density functional calculations. The structural and physicochemical properties of the pure metal and the alloy have been analyzed, and for Pt$_4$, the tetrahedral geometry is found to be more stable than the square planar geometry. On the optimized tetrahedral geometries the interactions of H$_2$, O$_2$, and CO with different orientations have been studied. The calculated energies of adsorption indicate H$_2$ and CO prefers to adsorb on Pt atop while O$_2$ prefers Co atop. The adsorption energy of CO is found to be the highest of all the three adsorbing species in both pure Pt$_4$ and Pt$_3$Co alloy clusters. [Preview Abstract] |
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D1.00102: Resonant charge transfer in H$^-$ ions scattering off Si(100) surfaces Boyan Obreshkov, Uwe Thumm We present numerical calculations on the one-electron charge exchange between an unreconstructed Si(100) surface and H$^-$ ions that are incident at kinetic energies of 1 keV. The ground state electronic structure of the surface is derived within a self-consistent screened pseudopotential Thomas-Fermi method. Si crystal wave functions and energies of the electron states that this potential holds are calculated by solving one-particle Schr\"{o}dinger equations. Resonant charge transfer ion-surface couplings are derived, and Newns-Anderson model is solved within a self-energy method. The neutralization probability of the anion after the collision is calculated and compared with available experimental data of [1]. \newline $[1]$ M.~Maazouz \emph{et al.} Surf.~Sci. {\bf 398}, 49 (1998). \newline \newline Supported by NSF and the Division of Chemical Sciences, Office of BES, Office of Energy, US DOE. [Preview Abstract] |
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D1.00103: ``Step-up" vs. ``Step-sown" scattering asymmetry in the charge transfer of H$^-$ on free-electron vicinal metallic surfaces Boyan Obreshkov, Uwe Thumm We present numerical results based on a wave-packet propagation study of the one-electron charge transfer between H$^-$ ions and free-electron vicinal metallic surfaces [1]. We derive an effective potential for the motion of the active electron within a Thomas-Fermi-von Weizs\"{a}cker model and extend this model to include the image charge effects. We first calculate H$^-$ affinity level shift and width in fixed-ion approximation and solve a rate equation for the ion-survival probability for projectiles that are incident with a kinetic energy of 50 eV. We find an enhancement of the electron loss near the steps of the surface, due to the Smoluchowski effect. As a consequence, the ion-survival is more likely if the projectiles approach steps from above than from below [2]. \newline \newline $[1]$ B.~Obreshkov and U.~Thumm, Phys. Rev. A {\bf 74}, 012901 (2006). \newline $[2]$ B.~Obreshkov and U.~Thumm, Surf. Sci. {\bf 601}, 622 (2007). \newline \newline Supported by NSF and the Division of Chemical Sciences, Office of Basis Energy Sciences, Office of Energy Research, US DoE. [Preview Abstract] |
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D1.00104: Three-state Feshbach resonances in the presence of external fields Christopher Hemming, Roman Krems We present an analytical analysis of Feshbach resonances involving three states in heteronuclear atom-atom collisions in the presence of external static electric and magnetic fields. The Hamiltonian of study involves a resonance coupling between a $p$-wave continuum state and a bound molecular state and a coupling between an $s$-wave continuum state and the $p$-wave continuum state. There is no direct coupling between the $s$-wave scattering state and the bound state of the dimer. The dependence of elastic $s$-wave scattering on the $s$-$p$ and $p$-bound couplings is described. [Preview Abstract] |
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D1.00105: Calculation of the dispersion interaction between two atoms J.-Y. Zhang, J. Mitroy, M.W.J. Bromley A general procedure for systematically evaluating the long range interaction between two hetero-nuclear atoms in arbitrary states is outlined. The $C_6$, $C_8$ and $C_{10}$ dispersion coefficients for the excited states of a number of alkali and alkaline atoms interacting with H and He are evaluated. One useful result concerns the lowest order $C_6$ coefficient for a pair of hetero-nuclear atoms. This can always be written in terms of sum rules only involving the oscillator strength. In addition, the coefficients for the long-range interaction between two homo-nuclear lithium atoms in a variety of excited states are presented. [Preview Abstract] |
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D1.00106: Non-adiabatic coupling in cold collisions of spin-polarized metastable hydrogen atoms Robert C. Forrey, Alex Dalgarno, Yulian V. Vanne, Alejandro Saenz, Piotr Froelich Previous calculations of low temperature cross sections for collisions between metastable hydrogen atoms are improved to include non-adiabatic radial and angular coupling. The electrostatic dipole-quadrupole interaction produces non-adiabatic radial coupling between (2s,2p) and (2p,2p) states while the Coriolis interaction produces non-adiabatic angular coupling. Both of these long-range contributions are handled in a space-fixed atomic gauge that is particularly convenient for a spin-polarized system. The improved theoretical results are compared with an existing experiment. [Preview Abstract] |
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D1.00107: H$_2$ dissociation due to collision with He Robert C. Forrey, N. Balakrishnan, Teck-Ghee Lee, Phillip Stancil Cross sections for dissociation of H$_2$ due to collision with He are calculated for excited rovibrational states using the quantum mechanical coupled states approximation. An $L^2$ Sturmian basis set with multiple length scales is used to to provide a discrete represention of the H$_2$ continuum which includes orbiting resonances and a non-resonant background. Cross sections are given over a range of translational energies for resonant and non-resonant dissociation together with the most important bound state transitions for four different initial states. The results demonstrate that it is possible to compute converged quantum mechanical cross sections using basis sets of modest size. [Preview Abstract] |
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D1.00108: Close-coupling study of rotational energy transfer in H$_2$O collisions with He atoms Benhui Yang, Phillip Stancil Due to the astrophysical importance of water and helium, the H$_2$O-He collisional system has been the subject of numerous experimental and theoretical studies. For numerical astrophysical models, quantitative determinations of state-to-state cross sections and rate coefficients for H$_2$O-He collisions are crucial. In this work quantum close-coupling scattering calculations of rotational energy transfer (RET) of rotationally excited H$_2$O due to collisions with He are presented for collision energies between 10$^{-6}$ and 1000 cm$^{-1}$ with para-H$_2$O initially in levels 1$_{1,1}$, 2$_{0,2}$, 2$_{1,1}$, 2$_{2,0}$, and ortho-H$_2$O in levels 1$_{1,0}$, 2$_{1,2}$, 2$_{2,1}$. Differential cross section, quenching cross sections and rate coefficients for state-to-state RET were computed on three new H$_2$O-He potential energy surfaces (PESs). The inelastic and elastic differential cross sections are also compared with available experimental measurements. [Preview Abstract] |
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D1.00109: A Two-Atom Relaxation-Theory Approach to Understanding Non-Markovian Dynamics in Dense Atomic Gases Josh W. Dunn, Chris H. Greene Relaxation theory, based on detailed treatment of atomic scattering, has in the past provided an elegant formalism [1] and yielded accurate predictions of experimental collisional-broadening data [2]. Recent experiments have utilized sophisticated transient four-wave-mixing techniques to probe interactions in dense atomic gases, and the use of fast lasers to create probe pulses allows for atomic collisions to be explored on a timescale shorter than the dephasing time of the gas [3]. We present a theoretical description of such phenomena that extends the relaxation-theory treatments beyond the regime of static collision broadening to the incorporate dynamical effects of transient photon-echo pulses. Beginning with a realistic description of two-atom scattering, we are able to calculate the nonlinear response function for the system, a quantity which can be compared with experimental photon-echo data. [1] U. Fano, Phys. Rev. \textbf{131}, 259 (1963). [2] A. Ben-Reuven, Phys. Rev. \textbf{145}, 7 (1966). [3] V. O. Lorenz and S. T. Cundiff, Phys. Rev. Lett \textbf{95}, 163001 (2005). [Preview Abstract] |
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D1.00110: SURFACE PLASMONS |
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D1.00111: Single-photon nonlinear optics with nano-scale surface plasmons Darrick Chang, Anders Sorensen, Vladimir Gritsev, Eugene Demler, Mikhail Lukin We explore nonlinear optical phenomena in systems that support a set of tightly-confined, one-dimensional electromagnetic modes. Among the physical systems of interest are guided surface plasmons propagating on conducting nano-structures and hollow-core photonic crystal fibers. The tight transverse confinement of the modes enables a large emitter-field coupling strength and the possibility of nonlinear optics down to a single-photon level. Several novel applications are presented. First, we demonstrate how the interaction between a single photon and either a single emitter or ensemble can be controlled to create a high-fidelity, state-dependent mirror. The state-dependent mirror can be used, for example, to implement a controlled-phase gate between photons or an all-optical, single-photon transistor. Connections to condensed-matter systems such as the Kondo Hamiltonian and Luttinger liquid are also discussed. [Preview Abstract] |
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D1.00112: Strong coupling of single optical emitters to nano-scale surface plasmons Aryesh Mukherjee, Alexey Akimov, Alexander Zibrov, Darrick Chang, Anders Sorensen, Chun Yu, Hongkun Park, Philip Hemmer, Mikhail Lukin We present an experimental observation of strong optical coupling between individual, nanocrystal CdSe/ZnS quantum dots and the guided surface plasmon modes of a proximal silver nanowire. The strong coupling between emitter and field is enabled by the unique properties of the plasmon modes on these nanowires. In particular, due to the small size of the nanowires (${\sim}100$ nm in diameter), the surface plasmons are localized transversely to dimensions well below the diffraction limit. An enhancement of the Purcell factor of the system and photon correlations consistent with a single-photon source are observed, and a realistic theoretical model for these processes is presented. [Preview Abstract] |
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D1.00113: Quantum Electrodynamics of Surface Plasmons J\'er\'emie Choquette, Peter Marzlin, Ren\'e Stock, Barry Sanders Surface plasmons are electromagnetically induced charge-density waves that appear at the interface between dielectrics and a thin metal film and can enhance optical field intensities by two to three orders of magnitude. Despite their fast decay surface plasmons have been shown to preserve optical entanglement and may be useful for optical quantum information. We present a detailed theoretical analysis of the interaction of photons and atoms in the presence of a dielectric interface permitting surface plasmons. We use a Green's function technique to quantize the electromagnetic field in planarly multi-layered lossy and absorbing dielectrics to give an accurate description of the noise induced near the metal film. We calculate the modified spontaneous emission rate of an atom near the interface and study the radiation characteristics of the emitted light. Furthermore we analyze the propagation of a single photon pulse through the interface. We discuss applications of our results to enhance nonlinear effects in quantum optics. [Preview Abstract] |
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D1.00114: ATOM MOTION/MATTER WAVE INTERFEROMETRY |
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D1.00115: Monte Carlo Simulation of Spontaneous Emission from Dressed States B. Barrett, S. Beattie, A. Kumarakrishnan It is well known that atomic states coupled with the photon field can be described by the dressed state basis. In previous work (J. Opt. Soc. Am. B \textbf{2}, 1707, Phys. Rev. A \textbf{47}, 2128) the atomic density matrix elements have been modeled in the dressed state basis, from which the spontaneous emission rates from dressed states can be calculated. We use this treatment to model the results of a recent experiment that uses a single state atom interferometer and laser cooled $^{85}$Rb atoms. The effective spontaneous emission rate measured in the experiment shows a monotonic increase as a function of ``interaction time''---the time atoms are subjected to standing wave laser pulses. We describe the details of the experiment and a Monte Carlo simulation of spontaneous emission from dressed states in a standing wave to explain the results. The results of the simulation show qualitative agreement with the experiment and suggest that the origin of the effect is related to the variation of the spontaneous emission rate in the standing wave potential and the spatial profile of the laser beams. [Preview Abstract] |
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D1.00116: Electron Coherence Length Measurement Using Nanogratings Ben McMorran, Alex Cronin We have measured the transverse coherence length of an electron beam using an electron interferometer constructed of two nanostructure gratings and an imaging detector$^1$. When one of the gratings is twisted about the optical axis the visibility of the Lau fringes decreases. This dependence is predicted by a theory that assumes a semi-coherent converging beam incident on two gratings. We present this theory along with data to show that the twist dependence of the fringe visibility is primarily sensitive to the transverse coherence length at the detector plane, in a direction parallel to the grating bars. $^1$A. Cronin and B. McMorran, \emph{Phys. Rev. A} \textbf{74},061602(R) (2006) [Preview Abstract] |
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D1.00117: Bose-Einstein condensates and their bright solitons in circular waveguides Martin D. Kandes, Oscar O. Salazar, Michael W.J. Bromley, Ricardo Carretero-Gonz{\'a}lez, Brett D. Esry Following the recent trapping and propagation of Bose-Einstein condensates around circular waveguides, we present theoretical results exploring some possible issues that may arise in future Sagnac interferometry experiments, particularly when perfect rings are tilted in gravity. We employ, firstly, a 1-D mean-field model to compare and contrast the interference observed when counterpropagating either BEC's, or continuously dispersion managed BEC's, or gap solitons. Secondly, we use 2-D simulations to determine the transverse excitations induced when splitting a curved wavepacket, either under instantaneous momentum transfer, or when the wavepacket is split using adiabatically raised potentials. We also present a simple classical model for the resultant amount of excitation which is valid for a range of experimentally accessible conditions. [Preview Abstract] |
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D1.00118: Sensitivity and accuracy studies of an atomic gravimeter Julien Le Gou\"et Atom interferometry is used to perform an absolute measurement of the gravitational acceleration $g$ with $^{87}$Rb free falling cold atoms. A sequence of three stimulated Raman transitions separates and recombines the atomic wave function, using vertical counter-propagating lasers. During each light pulse, the phase difference of the lasers is imprinted onto the atomic phase. The phase shift between the two paths depends on $g$, and scales with the square of the time interval between two consecutive pulses. As our experiment was developed to be transportable, the maximum interaction time is limited to 120 ms, but has a high repetition rate of up to 5 Hz. By combining passive isolation and post-treatment of the vibrations measurement, we reach a sensitivity better than $2\times10^{-8} g/Hz^{1/2}$. The contribution of the lasers to the phase noise of the interferometer is negligible, as it limits the sensitivity to $3\times10^{-9} g/Hz^{1/2}$. We pointed out a generally neglected effect due to the retro-reflection delay, which could represent a limitation to the sensitivity of atomic gradiometers. I will also detail our investigations of the various systematic effects that shift the measured value of g. Alternating measurements with opposite directions of the Raman lasers allows to reject shifts due to one photon light shift, RF phase shifts, as well as magnetic field gradients (rejection at the $10^{-3}$ level). The influence of two photon light shift, wavefront distortions and Coriolis acceleration will be discussed too. [Preview Abstract] |
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D1.00119: Enabling Chip-Based Atom Interferometry 1: Long Coherence Time and Number Squeezing with $^{23}$Na BECs C.A. Christensen, G.-B. Jo, Y. Shin, S. Will, T.A. Pasquini, M. Saba, W. Ketterle, D.E. Pritchard Using a combination of DC and RF magnetic fields, we have coherently split a BEC into two separated BECs on an atom chip. We find that the split BECs maintain a relative phase coherently for up to 200 ms, which we read out using absorption imaging of matter wave interference after time-of-flight expansion. This is a factor of 10 longer than the phase diffusion time for a coherent state at our atom number and density. We attribute the long coherence time to number squeezing by a factor of 10 caused by mean-field interactions during the splitting process, which reduces the phase diffusion rate. In spite of the presence of strong atom-atom interactions, the system potentially allows us to implement a BEC interferometer on an atom chip. G. --B. Jo et al., PRL 98, 030407 (2007) [Preview Abstract] |
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D1.00120: Enabling Chip-Based Atom Interferometry II: Working with Atom-Atom Interactions and Phase Fluctuations in Dense, Elongated Gases C.A. Christensen, G.-B. Jo, J.-H. Choi, T.A. Pasquini, Y.R. Lee, W. Ketterle, D.E. Pritchard BECs on atom chips tend to be dense and quite elongated. This leads to high mean-field interaction energy and phase fluctuations along the long dimension of the condensate. Interactions were expected to ``heal'' density imbalance and perturb coherent phase evolution, preventing reliable interferometry, while phase fluctuations across the sample may reduce signal-to-noise and imaging contrast. However, our experiments show that interactions promote long coherence time by number squeezing and enable in-situ phase readout by mapping the relative phase of separated BECs to the temperature of the system after merging. We also characterize phase fluctuations in our experiment, showing that they do not prevent reliable phase readout, but that they reveal an interesting regime of quasi 1-D degenerate gases. [Preview Abstract] |
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D1.00121: Effects of Light Scattering and Collisions on a Single State Atom Interferometer S. Beattie, I. Chan, A. Kumarakrishnan We have measured the effects of light scattering and collisions on the signal from a single state atom interferometer that uses laser cooled $^{85}Rb$. Two standing wave pulses separated by time $T$ are used to diffract and rephase momentum states (corresponding to the $F=3$ ground state) in the vicinity of $t=2T$. Light scattering and collisions reduce the timescale over which matter-wave interference can be observed. The decay rate of the signal is linearly proportional to the intensity of background standing wave light. The decay rate also scales inversely as the square of the detuning of the travelling components of the standing wave with respect to the $F=3 \rightarrow F=4$ transition. These observations are consistent with the scattering rate associated with a standing wave potential. By varying the vapour pressure of the background $^{85}$Rb vapour, we show that the experiment is sensitive to velocity changes of $\sim 100 \mu m/s$ and that the signal decay can be used to measure the cross section for hot-cold $Rb$ collisions. By characterizing decoherence effects it is possible to extend the timescale of the experiment to the transit time limit and carry out a precision measurement of the atomic recoil frequency. We review the current status of this experiment. [Preview Abstract] |
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D1.00122: Measurement of Gravitational Acceleration using a Single State Atom Interferometer C. Mok, S. Beattie, I. Chan, A. Kumarakrishnan We review the development of a gravimeter using a single state atom interferometer. Two standing wave pulses separated by $T$ are applied to a sample of laser cooled rubidium atoms. The first standing wave produces a density grating that is rephased in the vicinity of $2T$ by the second standing wave pulse. The rephased grating, known as an echo, is detected by coherently back scattering a traveling wave into a balanced heterodyne detector. The ratio of the in phase and quadrature components of the signal can be used to find the phase of the grating relative to an inertial reference frame. The accumulation of phase as a function of $T$ can be used to find $g$. Interestingly, the shape of the echo envelope contains temporal oscillations due to the Doppler shift, which can also be used to infer $g$. [Preview Abstract] |
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D1.00123: Quantum theory of atom lasers Tobias Kramer, Mirta Rodriguez Pinilla We present a three-dimensional, quantum mechanical and largely analytical theory for the properties of atomic laser beams in the gravitational field. The results describe both the total emission rate and the beam profile. Depending on the trapping frequencies and the strength of interactions, the theory predicts a transverse substructure in the atomic beam. Recent experiments on atom laser beam profiles are in good agreement with the model.\\ ~\\ References: T. Kramer and M. Rodriguez\\ Quantum theory of an atom laser originating from a Bose-Einstein condensate or a Fermi gas in the presence of gravity\\ Phys. Rev. A, 74, 013611-1-13, (2006) [Preview Abstract] |
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D1.00124: Coherent Slowing of a Pulsed Supersonic Beam with an Atomic Paddle Adam Libson, Edvardas Narevicius, Max Riedel, Christian Parthey, Isaac Chavez, Uzi Even, Mark Raizen We report the slowing of a supersonic beam by elastic reflection from a receding atomic mirror. Supersonic beams, formed by the adiabatic expansion of high pressure gas through an aperture, are currently the highest brightness sources available and have a high degree of monochromaticity. We use a pulsed supersonic nozzle to generate a 511 $\pm $ 9 m/s beam of helium that we slow by reflection from a Si(111)-H(1x1) crystal placed on the tip of a spinning rotor. We are able to continuously reduce the velocity of helium by 246 m/s and show that the temperature of the slowed beam is lower than 250 mK in the co-moving frame. We plan to use this beam as a probe for surface science studies and as the source for atom optics and interferometry experiments. The slow, cold, and intense nature of the beam should open new energy ranges and resolutions, allowing higher precision measurements. [Preview Abstract] |
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D1.00125: Controlling atomic motion in optical billiards J. L{\'e}pine, G. Painchaud-April, J. Poirier, L. J. Dub{\'e} We present different scenarios to control atomic motion in optical billiards [1] under conditions where classical chaos is present. Since the billiard boundary is drawn with appropriately deflected beams of light, giving rise to an effective static potential barrier, the motion of the enclosed atoms can be influenced by judiciously chosen small dynamical deviations of the scanning beams. We in fact demonstrate, by realistic numerical simulations, that the, otherwise chaotic behaviour, can be controlled and made stable and predictable. By selecting different cavity shapes (stadium, multipolar deformations of the circle, (smoothed) polygons etc.), we study our stabilization approaches under conditions ranging from mixed to fully chaotic dynamics and analyse the effects of soft boundaries and imperfections on the robustness of the control techniques. This acquired controlled ability offers a new tool for testing fundamental questions at the border of classical and quantum chaos. \\ {\ }\\ {[1]} V. Milner {\em et al.}, Phys.Rev. Lett. {\bf 86}, 1514 (2001) ; N. Friedman {\em et al.}, Phys. Rev. Lett. {\bf 86}, 1518 (2001). [Preview Abstract] |
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D1.00126: CONDENSED MATTER PHYSICS |
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D1.00127: Photoconductivity of Yttrium Praseodymium Gadolinium Oxalate Crystals Soosy Kuryan, Rosalin Abraham, Jayakumari Isac Crystals are pillars of modern technology. Yttrium Praseodymium Gadolinium oxalate (YPrGaOx) crystals were grown by gel method by the diffusion of Yttrium Chloride, Praseodymium Chloride, and Gadolinium Chloride into the set gel containing Oxalic acid. Silica gel method is capable of yielding crystals of high optical perfection and wide morphology. The growing crystals are held in the gel medium in a strain free manner and at the same time nucleation and super saturation are well controlled. Photo conductivity studies of these crystals revealed negative photoconductivity nature. The photocurrent is found to be less than the dark current at every applied electric field. Rare Earth compounds are known for their interesting electric, magnetic and luminescent properties. Recent investigations on the fluorescence of some rare earth oxalates suggest their potentiality for their optical applications. Rare Earth oxalates evoked greater attention because of their ionic conduction. [Preview Abstract] |
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D1.00128: ABSTRACT WITHDRAWN |
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D1.00129: Optical properties of vanadium doped ZnTe thin cermet films Khairul Alam Khan, M. Sazzad Hossain, M. Rezaul Islam ZnTe:V thin cermet films (containing 0 to 10wt{\%} V in ZnTe matrix) were prepared onto glass substrate by e-beam evaporation in vacuum at $\sim $0.0001 Pa. The deposition rate of the films was at about 2.05 nm/s. The effects of various deposition conditions on the electrical and optical properties of the cermet films have been studied in detail. The structure analysis of the film was performed by X-ray diffraction technique and it was found that the films are amorphous in nature. The optical properties of both the as-deposited and annealed films were studied in the wavelength range 300$<$lambda$<$2500 nm, respectively. For both types of cermet sample, the values of Urbach tail, optical band gap, refractive index and dielectric constants were evaluated for different compositions and thicknesses, respectively. Evaluation of these parameters may help in view of their technological applications in selective surface as well as in optoelectronic devices. [Preview Abstract] |
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D1.00130: Magnetic Field Noise from High Permeability Magnetic Shields for Precision Measurements S.-K. Lee, S.J. Smullin, T.W. Kornack, M.V. Romalis High permeability magnetic shields often generate magnetic field noise that can limit the sensitivity of precision measurements. We show that calculations based on the fluctuation-dissipation theorem allow evaluation of magnetic field noise, either by current or spin fluctuations, from high permeability metals and ferrites over a broad frequency range. For example, the noise spectrum of a mu-metal shield generally exhibits three distinct frequency dependent behaviors: low frequency 1/f spin noise, white noise due to Johnson noise current, and high frequency roll-off due to self-shielding. To reduce the effect of Johnson noise current, we built a multi-layer shield for a potassium SERF atomic magnetometer using ferrite for the innermost layer. We found that the white noise was reduced from about 20 fT/Hz$^{1/2}$, as expected for an all-mu metal shield, to 0.75 fT/Hz$^{1/2}$, limited by laser noise. The low frequency 1/f noise agreed well with calculation based on the measured complex permeability of the ferrite. Our method can be used to identify low noise shielding materials for further suppression of shield-generated noise for compact atomic magnetometers. [Preview Abstract] |
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