Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session L6: Atomic and Molecular Structure and Properties I |
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Chair: Marjatta Lyyra, Temple University Room: Knoxville Convention Center 301C |
Thursday, May 18, 2006 10:30AM - 10:42AM |
L6.00001: Two-Photon Coherent Atomic Absorption of Multiple Laser Beams Ming-Chiang Li Physical processes on two-photon coherent atomic absorption of multiple laser beams were discussed about thirty years ago [M. C. Li, Bull. Am. Phys. Soc. 20, 654 (1975)]. These processes can be divided into two distinct groups. In the first group, laser beams are from a single source, and in the second group laser beams are from two different sources [M. C. Li, \textit{Phys. Rev. A }\textbf{22 }(1980) 1323]. Several experiments in the first group were carried out and have led to the 2005 Nobel Prize in physics. The second group is more interesting. Beside atoms are in random motion, two photons are from different sources. Classically, it is impossible for atoms to transit coherently in the absorption process, but quantum mechanically, such a transition is possible and that is one of the spooky phenomena in quantum mechanic. To assure the coherent transition, each photon as absorbed by the atom must have two possible paths of choices. If one photon has the choice and other one is not, then the atomic transitions cannot be coherent. Around1990, there were very active experimental pursuits on such a spooky phenomenon of two photons emitted from crystal parametric down conversion. The present talk will review various spooky phenomena associated with two-photon coherent atomic absorption. Hope that the talk will stimulate the interest on the long neglected experimental front on two-photon coherent atomic absorption from two different laser sources. [Preview Abstract] |
Thursday, May 18, 2006 10:42AM - 10:54AM |
L6.00002: Coarse-grained entropy decrease and novel phase-space focusing and cooling in Hamiltonian dynamics Arjendu Pattanayak, Daniel W.C. Brooks, Anton de la Fuente, Lawrence Urrichio, Edward Holby, Daniel Krawisz, Jorge Silva We analyze the behavior of the coarse-grained entropy for classical probabilities in nonlinear Hamiltonians. We focus on the result that if the trajectory dynamics are integrable, the probability ensemble shows transient increases in the coherence, corresponding to an increase in localization of the ensemble and hence the phase-space density of the ensemble. We discuss the connection of these dynamics to the problem of cooling in atomic ensembles. We show how these dynamics can be understood in terms of the behavior of individual trajectories, allowing us to manipulate ensembles to create ``cold'' dense final ensembles. We illustrate these results with an analysis of the behavior of particular nonlinear integrable systems, including discussions of the spin-echo effect and the seeming violation of Liouville's theorem. [Preview Abstract] |
Thursday, May 18, 2006 10:54AM - 11:06AM |
L6.00003: Non-linear Optical Rotary Dispersion of Crystalline NaClO$_{3}$ and NaBrO$_{3 }$ and Uridine Solutions Andrew Fischer, Richard Pagni, Robert Compton, Jingguo Yang Sodium chlorate (NaClO$_{3})$ and sodium bromate (NaBrO$_{3})$ form chiral crystals belonging to the P2$_{1}$3 space group for which the same crystal structures exhibit \textit{opposite} optical rotation. The uridine molecule is an inherently chiral molecule and has been studied in aqueous solutions. We report optical rotary dispersion (ORD) curves from 700-475 nm for both of the chiral crystals and uridine solutions using an OPO laser. The measured non-linear optical rotation for sodium chlorate and sodium bromate is found to increase with increasing light intensity over the range of 1064 to 532 nm. Changes in the optical rotation as a function of laser power (non-linear ORD, NL ORD) are measured using the fundamental (1064 nm) harmonics (532 nm, 355 nm) of a Nd:YAG laser . These results will be compared with the previously reported NL ORD studies [\textit{Mol. Phys}. 1997 for uridine in H$_{2}$O solutions in which the OR is reported to decrease with increasing laser intensity. For the limited data available, it appears that the NL ORD is determined by the OR at the dominant n-photon region. [Preview Abstract] |
Thursday, May 18, 2006 11:06AM - 11:18AM |
L6.00004: Effects of Frequency Chirping in Electro-Magnetically Induced Transparency Frank A. Narducci, Jon P. Davis Under the right conditions, electro-magnetically induced transparency can lead to ultra-narrow resonances. In this paper, we explore theoretically the effects of rapidly chirping the frequency of the probe laser on the observed lineshapes. For a proper choice of parameters, the lineshape can become distorted and show asymmetric ringing-like behavior. Experimental results will also be discussed. [Preview Abstract] |
Thursday, May 18, 2006 11:18AM - 11:30AM |
L6.00005: Coherent Molecular Vortex Generation from an Atomic Condensate H. Ling, D. Grochowski, S. Yi, H. Pu, Weiping Zhang We consider a two-color photoassociation model in a field configuration in which the dump field is in a Gaussian mode while the pump field is in a first-order Laguerre Gaussian mode. We show that this configuration supports a nonlinear dark state, which is a coherent superposition between an atomic BEC and the ground molecular vortex state of winding number 1. We use this nonlinear dark state as the basis for developing a chipped stimulated Raman adiabatic passage that can lead to an efficient conversion of an atomic condensate into a ground molecular vortex while minimizing the particle loss via the excited molecular state. [Preview Abstract] |
Thursday, May 18, 2006 11:30AM - 11:42AM |
L6.00006: Effect of optical lattice and microwave fields on the formation and confinement of ultracold molecules Svetlana Kotochigova, Eite Tiesinga Our goal is to estimate the effect of optical lattice fields on photoassociative formation of ultracold molecules from their atoms. We examine production of translationally cold molecules by considering a stimulated Raman process to specific intermediate ro-vibrational levels of excited states. We propose that for photoassociation in a lattice the effect of excited state spontaneous decay can be strongly diminished. We also investigate the interaction of polar molecules with optical lattices and microwave fields. We theoretically demonstrate the existence of frequency windows in the optical domain where the complex internal structure of the molecule does not influence the trapping potential of the lattice. In such frequency windows the Franck-Condon factors are so small that near-resonant interaction of vibrational levels of the molecule with the lattice fields have a negligible contribution to the polarizability and light-induced decoherences are kept to a minimum. In addition, we show that microwave fields can induce a tunable dipole-dipole interaction between ground-state rotationally symmetric molecules. A combination of a carefully chosen lattice frequency and microwave-controlled interaction between molecules will enable trapping of polar molecules in a lattice and possibly realize molecular quantum logic gates. [Preview Abstract] |
Thursday, May 18, 2006 11:42AM - 11:54AM |
L6.00007: Characterization of statistical properties of x-ray FEL radiation by means of two-photon processes Nina Rohringer, Robin Santra The pulsed radiation from a free-electron laser (FEL) in the self-amplified spontaneous emission mode changes its time-dependent electric field from shot to shot in a completely chaotic fashion. For experiments in the x-ray regime with data acquisition over several FEL pulses, the characterization of the statistical properties of the radiation is essential, i.e.\ spectral or time correlation functions of the electrical field have to be determined. By treating the matter-field interaction perturbatively within a quantum electrodynamic framework, we determine the relevant correlation functions for one- and two-photon processes, i.e.\ for single and double photon absorption and elastic scattering. The radiation field is described by a general multi-mode density matrix. The possibility of utilizing two-photon-induced double ionization to determine the second-order spectral correlation function of the radiation field is discussed. Considering the example of helium we study the two-photon absorption probability in dependence of spectral correlation functions estimated for different FEL electron-bunch geometries and compare them to signal strength obtained from a single-mode field and from totally chaotic, incoherent x-ray radiation. [Preview Abstract] |
Thursday, May 18, 2006 11:54AM - 12:06PM |
L6.00008: Recombination and ionization cross sections for all ion stages of argon. Sh. A. Abdel-Naby, S.D. Loch, M.S. Pindzola, N.R. Badnell We present a range of ionization and recombination cross section calculations for all ionization stages of argon, for application in tokamak plasma disruption mitigation studies. The ionization cross sections are evaluated in a configuration-average distorted-wave (CADW) approach, benchmarking against experiment for the lower ion stages. The CADW cross sections are also compared with more accurate level-resolved distorted-wave calculations. The dielectronic-recombination cross sections are also evaluated in a CADW approach for all ion stages for $\Delta n =0$ and $\Delta n = 1$ core excitations. These cross sections are compared with more accurate level resolved distorted-wave results for ion stages Ar$^{6+}$ through to Ar$^{17+}$. We use this comparison as a means of estimating the accuracy of the CADW method for ion stages Ar$^{+}$ through to Ar$^{5+}$, which are currently beyond the reach of level-resolved perturbative methods. We also compare with various semi-empirical approaches for these ion stages. The atomic cross sections are processed into Maxwellian rate coefficients for use in plasma modeling. [Preview Abstract] |
Thursday, May 18, 2006 12:06PM - 12:18PM |
L6.00009: On the Structure of the SF$_{6}^{-}$ Anion Jeffrey Steill, Robert Compton, K. Bowen, Sarah Stokes Negative ions of Sulfur hexafluoride have been studied in detail for decades; however, there remains much to be understood about this subject. The geometry of SF$_{6}^{- }$in its ground state is either of O$_{h}$ symmetry like the parent molecule, or of a distorted C$_{4v}$ symmetry. The lower symmetry form with an elongated axial S-F bond is predicted by Coupled-Cluster computational methods to be lower in energy by about 0.1 eV. The calculated frequencies for the two different geometries are significantly different, providing a possible means for a definitive structure determination. Photoelectron spectra of vibrationally relaxed SF$_{6}^{- }$give an EA of 1.0 (+/- 0.1) eV with a very broad energy spectrum, implying a significant geometry change from the neutral to the anion. This suggests the C4v form may be the likely geometry. Quasi-equilibrium theory calculations of the lifetime of SF$_{6}^{- }$ using the calculated frequencies for the anion combined with the known electron attachment rates gives a mean lifetime on the order of one millisecond. This lifetime is much larger than the lifetime derived from TOFMS methods, which is on the order of microseconds. The vibrational structure in the PES spectra is compared to the calculated frequencies for both of the possible geometries, but does not provide a completely unambiguous assignment. Therefore, we will also describe our recent attempts to measure the vibrational spectrum of gas-phase SF$_{6}^{- }$. [Preview Abstract] |
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