Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session R1: Poster Session III: 4:00 pm - 6:00 pm |
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Room: HUB-Robeson Center Alumni Hall |
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R1.00001: SPECTROSCOPY, LIFETIMES, OSCILLATOR STRENGTHS |
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R1.00002: Precise measurements of hyperfine structure and atomic polarizability in indium and thallium using two-color diode laser spectroscopy Mevan Gunawardena, P.W. Hess, P.K. Majumder We are pursuing a series of precise atomic structure measurements in atomic thallium and indium designed to test new \textit{ab initio} theory calculations in these three-valence-electron systems [Phys. Rev. A 74, 022504 (2006); Phys. Rev. A 76, 022501 (2007)]. For thallium, independent atomic theory calculations are essential for atomic tests of symmetry violation. In one experiment, using two-color laser excitation, the hyperfine constants of the 6P$_{3/2}$ excited state of indium(I=9/2) have been measured for the first time. We excite ground-state atoms to the 6S$_{1/2}$ state using a stabilized 410 nm diode laser system. A second laser beam at 1291 nm overlaps the blue beam in a heated indium vapor cell, driving Doppler-narrowed hyperfine transitions to the 6P$_{3/2}$ excited state. By modulating the blue laser beam and using lock-in detection, we obtain background-free, low-noise IR spectra. Current statistical precision is at the MHz level, and preliminary results agree well with theory predictions for the hyperfine constants. Using a similar excitation scheme in our thallium atomic beam apparatus, we are undertaking to measure the Stark shift of the thallium 1301 nm 7S$_{1/2 }$- 7 P$_{1/2}$ transition by first driving the 378 nm 6P$_{1/2}$ - 7S$_{1/2 }$ transition using a stabilized UV laser diode system. [Preview Abstract] |
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R1.00003: Cesium $7d \, ^2 \! D_{3/2}$ hyperfine coupling constants measured using two-photon fluorescence spectroscopy of a thermal beam V. Fiore, A. Kortyna The hyperfine intervals of the $^{133}$Cs $7d \, ^2 \! D_{3/2}$ manifold are determined through resonant two-photon, laser-induced-fluorescence spectroscopy. These intervals are used to calculated the magnetic dipole coupling constant, $A$, and the electric quadrupole coupling constant, $B$. Two single-mode, external-cavity diode lasers counter-propagate through a thermal beam of cesium. A servo-feedback circuit locks one laser to the $6s \, ^2 \! S_{1/2} (F) \rightarrow 6p \, ^2 \! P_{1/2} (F')$ transition. The second laser is scanned over the $6p \, ^2 \! P_{1/2} (F') \rightarrow 7d \, ^2 \! D_{3/2} (F'')$ transitions. Its relative frequency is calibrated through a phase modulation technique, and high accuracy is achieved by referencing the modulation frequency in real time to the $^{87}$Rb $5s \, ^2 \! S_{1/2} (F=1) \leftrightarrow 5s \, ^2 \! S_{1/2} (F=2)$ ground state hyperfine transition using an atomic frequency standard. The $7d \, ^2 \! D_{3/2}$ hyperfine intervals are found through non-linear fitting of Voigt profiles to the fluorescence spectra, and give the hyperfine coupling constants $A = 7.38 \pm 0.04 \,$MHz and $B = -0.06 \pm 0.26 \,$MHz. The magnetic dipole constant, $A$, agrees well with a previously measured value of $7.4 \pm 0.2 \,$MHz (G. Belin et al., Phys.\ Scr.\ {\bf 14}, 39 (1976)). [Preview Abstract] |
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R1.00004: Laser Spectroscopy of Rydberg Level Hyperfine Structure Investigations in Niobium I S.~Bur\c{c}in Bayram, G\"{u}nay Ba\c{s}ar, G\"{o}n\"{u}l Ba\c{s}ar, Sophie Kr\"{o}ger We have applied high-resolution laser spectroscopic techniques to measure the hyperfine structure of the high-lying levels of atomic niobium: 20 well-resolved spectra were measured using Doppler-limited optogalvanic spectroscopy technique and 10 spectra using Doppler-reduced saturation absorption spectroscopy technique in the wavelength range between 645~nm and 675~nm. We have precisely determined the magnetic dipole hyperfine structure constants $A$ for 42 levels and electric quadrupole hyperfine structure constants $B$ of 15 levels. 17 $A$ constants and 5 $B$ constants were measured for the first time. With the present work the experimental hyperfine data for the levels of odd parity of atomic Nb is extended. [Preview Abstract] |
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R1.00005: Trapping and Spectroscopy of Singly- and Doubly-charged Ytterbium Ions Martin Schauer, Justin Torgerson, David Feldbaum, Tuan Nguyen, LiBang Wang, Xinxin Zhao Forbidden optical transitions in Ytterbium ions have been shown to possess both high sensitivity to possible time variation of the Fine Structure Constant and low sensitivity to external field perturbations. Of specific interest in this regard are the $^{1}$S$_{0}$ -- $^{3}$P$_{0}$ transition in Yb$^{2+}$ and the $^{2}$S$_{1/2}$ -- $^{2}$D$_{3/2}$ electric quadrupole transition in Yb$^{+}$. We describe recent progress in trapping Yb$^{2+}$ and report on initial spectroscopic work on Yb$^{+}$ and Yb$^{2+}$. [Preview Abstract] |
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R1.00006: Precision Lifetime Measurement of the Cesium 6$P_{3/2}$ State Jerry Sell, Austin Bergstrom, Brian Patterson, Randy Knize, Thomas Ehrenreich We will report a precision measurement of the cesium 6$P_ {3/2}$ atomic state lifetime using a refinement of our lifetime measurement technique.\footnote{B.M. Patterson, C.D. Lindstrom, T. Takekoshi, J.R. Lowell, C. Villarreal, and R.J. Knize, Opt. Lett. \textbf{28} (19), 1814 (2003).} Initially a single pulse ($\sim$ nJ) is selected from a mode-locked Ti:Sapphire laser which excites cesium atoms in counter-propagating thermal beams to the 6$P_{3/2}$ state. A subsequent laser pulse is amplified in a regenerative amplifier ($\sim$ $\mu$J) and also frequency doubled, resulting in pulses which nonresonantly ionize the cesium atoms if they have been excited to the 6$P_{3/2}$ state. The ions are collected and counted while varying the delay between the excitation and ionization pulses allowing us to measure the excited state lifetime. We will also address the dominant systematic errors which include: effects from the misalignment of the excitation and ionization laser beams, imperfect extinction ratio of the electro-optic modulators used for pulse selection, and the effect of quantum beats. Finally we consider extending these lifetime measurements to different cesium states and different atoms. [Preview Abstract] |
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R1.00007: Observed Suppression of an E1 Allowed Transition in $^3$He Michael Bishof, Ibrahim Sulai, Zheng-Tian Lu, Kevin Bailey, Peter Mueller, Tom O'Connor, Gordon W.F. Drake, Qixue Wu Many instances occur when hyperfine mixing enhances the strength of forbidden transitions, such as ground state to $^3$P$_0$ transitions in odd isotope alkaline earths. However, strong suppression of an allowed transition due to hyperfine mixing is rare. We have observed strong suppression of the E1 allowed 2$^3$S$_1$ F=3/2 to 3$^3$P$_1$ F=3/2 transition in $^3$He. In a theoretical model developed by Drake et al., this ``missing'' transition is attributed to hyperfine mixing of the 3$^3$P$_1$ F=3/2 and 3$^3$P$_2$ F=3/2 states. The theoretical model also predicts the magnetic field dependence of transition strength for the ten transitions between magnetic sublevels of 2$^3$S$_1$ F=3/2 and 3$^3$P$_1$ F=3/2. We present measurements of this dependence using laser spectroscopy at 389nm on a collimated beam of metastable $^3$He atoms. [Preview Abstract] |
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R1.00008: Hyperfine Suppression of a $2\;^3$S$_1$ -- $3\;^3$P$_1$ Radiative Transition in Helium Qixue Wu, Gordon W.F. Drake In $^3$He, we have found both experimentally and theoretically that the electric dipole radiative transition $2\;^{3}$S$_{1} (F=3/2) $ to $3\;^{3}$P$_{1} (F= 3/2)$ between hyperfine states is strongly suppressed. The suppression is caused by strong hyperfine mixing and accidental cancellation between two hyperfine states with different $J$ but the same $F$ in the $3\;^{3}$P state. We present high precision variational calculations in Hylleraas coordinates of the line strength, including hyperfine mixing, and compare the results with experiment. The influence of a weak magnetic field up to 100 gauss on the line strength provides an additional test of this hyperfine suppression phenomenon. Theoretical calculations show that a maximum suppression occurs for the Zeeman component $2\;^{3}$S$_{1} (F= 3/2,\,M_F=-1/2)$ to $3\;^{3}$P$_{1} (F= 3/2,\,M_F=-1/2)$ of the hyperfine transition at approximately 65 gauss. Theoretical and experimental studies of other $n\;^3$P states are in progress to check for other similar suppression effects in $^3$He. [Preview Abstract] |
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R1.00009: Two-photon lock by ground state phase-modulation transfer in rubidium. Adrian Perez Galvan, Dong Sheng, Luis Orozco We present a method to lock on resonance the second step of the 5S$_{1/2}\rightarrow$5P$_{3/2}\rightarrow$5D$_{5/2}$ two-photon transition at 776 nm in rubidium by monitoring the changes of population of the 5S$_{1/2}$ ground state in a vapor cell. The low probability of excitation in the two-step atomic transition makes the direct observation of population in the final excited state i.e. changes in absorption of the second laser as a function of frequency, very difficult. Monitoring the ground state population instead increases the signal to noise ratio of the two-photon signal. The decrease of the stringent experimental conditions suggests combining the detection method with one of many one-photon spectroscopy techniques. A density matrix model explains well the behaviour of the signal and we show phase sensitive detection of the frequency modulated laser at 780~nm laser as a function of the frequency of the second photon to lock the modulation-free 776~nm laser. [Preview Abstract] |
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R1.00010: Atomic Spectra Bibliography Databases at NIST Alexander Kramida NIST's Atomic Spectroscopy Data Center maintains three online 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] now includes about 11500 references, mostly for years 1967--2007. The NIST Atomic Transition Probability BD, v.~8.1 [http://physics.nist.gov/fvalbib] with its 7500 references mainly covers years 1964--2007. The NIST Spectral Line Broadening BD, v.~2.0 [http://physics.nist.gov/linebrbib] has 3670 references, mostly for 1978--2006. All three databases are maintained in a unified database management system that allows us to quickly update the contents. Updates become available to users on the next day. An automated Data Entry module makes it easy to enter and categorize the data. The system allows us to keep the contents of all BDs up to date. A number of enhancements made since last year greatly increased public usability of the databases. This work is supported in part by the Office of Fusion Energy Sciences of the U.S. Department of Energy and by the National Aeronautics and Space Administration. [Preview Abstract] |
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R1.00011: Pressure broadening of potassium by helium and by molecular hydrogen J.F. Babb, K. Kirby, F. Shindo Absorption around the wavelengths of the resonance lines of potassium pressure broadened by helium and by molecular hydrogen is an important contributor to the opacities of late-type brown dwarfs. Satellite features appearing in the far wings of the absorption profiles are of interest as possible tests of atmospheric models. We report on experimental and theoretical studies of the first and the second resonance lines of potassium broadened by He and by molecular hydrogen. [Preview Abstract] |
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R1.00012: Spectra of Highly Ionized Hf, Ta, W, and Au Observed with an EBIT Light Source Ilija N. Draganic, Yuri Ralchenko, John D. Gillaspy, Joseph N. Tan, Joshua M. Pomeroy, Joseph Reader We observed spectra of highly-ionized Hf, Ta, W, and Au in the region 4-20 nm with the NIST EBIT and grazing incidence spectrograph. Stages of ionization were distinguished by varying the beam energy. Ionization stages of 37+ to 56+ were typically observed. The spectra were calibrated by separate spectra of highly ionized iron. Line identifications were carried out with use of collisional-radiative modeling of the EBIT plasma. Many new lines were identified for each element. Good quantitative agreement between simulated spectra and the observations was obtained. [Preview Abstract] |
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R1.00013: Atomic data for dielectronic satellite lines and dielectronic recombination into Ne$^{5+}$ R. Mancini, U.I. Safronova Energy levels, radiative transition probabilities, and autoionization rates for B-like neom Ne$^{5+}$ including $1s^22s^2nl$, $1s^22s2pnl$, and $1s^22p^2nl$ ($n$=2-11, $l = s, p, d, f, g, h, i, k$ ) states were calculated by multi-configurational Hartree-Fock method (Cowan code) and relativistic many-body perturbation theory method (RMBPT) code. Autoionizing levels above three thresholds ($1s^22s^2\ ^1S$, $1s^22s2p\ ^3P$, $1s^22s2p\ ^1P$) were considered. Branching ratios relative to the first threshold and intensity factor were calculated for satellites lines and dielectronic recombination rate coefficients for the excited 190 odd-parity and 198 even-parity states. The dielectronic recombination rate coefficients including $1s^22s^2nl$, $1s^22s2pnl$, and $1s^22p^2nl$ ($n$=2-11, $l= 0-7 $) states were calculated. The contributions from the excited states higher than $n$=11 were estimated by extrapolation of all atomic characteristics to derive the total dielectronic recombination rate coefficient. The orbital angular momentum quantum number $l$ distribution of the rate coefficients shows a peak at $l$=5. The total dielectronic recombination rate coefficient was derived as a function of electron temperature. The dielectronic satellite lines were also obtained. [Preview Abstract] |
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R1.00014: Simulation and Spectroscopy of highly charged Krypton Plasmas Arati Dasgupta, Robert Clark, John Giuliani, Jack Davis We will analyze the sensitivity of atomic models for K- and L-shell krypton by investigating its impact on radiation from a cylindrical static plasma of specified internal energy. Our atomic model employs an extensive atomic level structure, which is necessary to accurately model the pinch dynamics and the spectroscopic details of the emitted radiation. The atomic data is obtained using the state-of-the-art Flexible Atomic Code, and all relevant radiative atomic processes are included in generating the model. The enormous number of fine-structure levels are judiciously lumped to create a database that is detailed but appropriately sized for future use in hydrodynamic simulation of Z-pinches. We will compare and contrast the results with those obtained using previous krypton atomic models which have limited structure. We will explore the behavior in the krypton ionization stages and emitted synthetic spectra using temperature and density conditions that have been predicted in 1-D calculations of implosions on the Sandia ZR accelerator. [Preview Abstract] |
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R1.00015: 2p$_{3/2}^{-1}$3x$^{-1}$-3x$^{-1}$4d$^{-1}$ X-Ray Satellites spectra in the L$\beta _{2 }$region Surendra Poonia The X-ray satellite spectra arising due to 2p$_{3/2}^{-1}$3x$^{-1}$-3x$^{-1}$4d$^{-1}$ (x $\equiv $ s, p, d) transition array, in elements with Z = 42 to 90, have been calculated. While the energies of various transitions of the array have been determined by using available Hartree-Fock-Slater data on 1s$^{-1}$-2p$^{-1}$3x$^{-1}$ and 2p$_{3/2}^{-1}$-3x$^{-1}$,3x'$^{-1}$ Auger transition energies, their relative intensities have been estimated by considering cross sections of singly ionized 2x$^{-1}$ (x $\equiv $ s, p) states and then of subsequent Coster-Kronig and shake off processes. The calculated spectra have been compared with the measured satellite energies in L$\beta _{2}$ spectra. Their intense peaks have been identified as the observed satellite lines. It has been established that four satellites observed in the L$\beta _{2 }$region of the X-ray spectra of various elements and named $\beta _{2}^{I}$, $\beta _{2}^{(b)}$, $\beta _{2}^{II}$ and $\beta _{2}^{(c)}$ in order of increasing energy are mainly emitted by 2p$_{3/2}^{-1}$3d$^{-1}$-4d$^{-2}$ transitions. In the present study, we report the transition assignments to the satellites $\beta _{2}^{I}$, $\beta _{2}^{(b)}$, $\beta _{2}^{II}$ and $\beta _{2}^{(c)}$ reported in the spectra of elements with Z = 42 to 52 and the satellites named $\beta _{2}^{I}$ and $\beta _{2}^{II}$ in the L - emission spectra of the elements of $_{74}$W to $_{90}$Th. It is observed that out of these four satellites, $\beta _{2}^{(b)}$ can be assigned to superposition of $^{3}$F$_{4}-^{3}$G$_{5}$ and $^{3}$F$_{4}-^{3}$D$_{3}$ transitions and that this must be the most intense of all these satellites in the elements Z = 42-50. In the range of elements Z = 52 to 77, the satellite $\beta _{2}^{I}$ is emitted by these transitions. [Preview Abstract] |
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R1.00016: Anomalous behavior of Auger and radiative rates and fluorescence yields along the $1s2s^22p^{3}$ K-shell isoelectronic sequence Muhammet Fatih Hasoglu, Dragan Nikoli\'c, Thomas W. Gorczyca, Steven T. Manson, Mau Hsiung Chen, Nigel Badnell Calculations using two different methodologies have revealed anomalous behaviour of the radiative and Auger rates, and the associated fluorescence yields, of the six electron $1s2s^22p^{3}$ K-shell vacancy isoelectronic sequence as a function of $Z$ from the neutral to $Z$ of 30. This behavior is explained in terms of an accidental degeneracy, an avoided-crossing of two nearly-degenerate spin-orbit coupled states. The results also demonstrate the importance of including both multielectron correlation and spin-orbit effects even at low- $Z$, and that interpolation of computed fluorescence data is inaccurate in general. [Preview Abstract] |
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R1.00017: The effect of approximations on atomic emission spectra Justin Oelgoetz, Christopher J. Fontes, Hong Lin Zhang, Anil K. Pradhan Atomic kinetics modeling is essential if we are to understand the spectroscopy of astrophysical objects. In order to model astrophysical spectra, one must first calculate the electronic structure of the ions, calculate cross sections and rates for the processes in between the resulting levels (and ionization stages), and then solve a set of coupled collisional-radiative equations that depend on the plasma conditions. Spectra are ultimately created from the solutions to these collisional-radiative equations. The aim of this work is to benchmark the impact of some of the typical approximations employed in this modeling process. We will present results that illuminate the effects of approximations in the structure calculations (fine-structure approaches, which include configuration interaction, vs. configuration-average approaches), and in the cross section calculations (by comparing the results of data calculated using close-coupling R-Matrix method, distorted-wave methods, as well as other more approximate scaled-hydrogenic and plane-wave-Born methods). [Preview Abstract] |
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R1.00018: THE ULTRA INTENSE LASER FRONTIER (STRONG FIELD, INTENSE LASER PROCESSES) |
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R1.00019: The Role of Mass in the Carrier-Envelope Phase Effect for $\rm H_2^+$ Dissociation Jianjun Hua, Brett Esry The field-aligned model in the Born-Oppenheimer representation is adopted to study carrier-envelope phase (CEP) effects in the dissociation of $\rm H_2^+$ and its isotope $\rm D_2^+$ in an intense laser field. We find that $\rm D_2^+$ shows larger CEP effects under the same laser conditions. Specifically, the CEP effects appear as differences in each dissociation channel $\rm{p+H}$ and $\rm{H+p}$, i.e. p going up or down, respectively, relative to the laser polarization direction.We will present results for a range of laser intensities, and we will also present an interpretation based on the recently developed theory in Ref. [1]. [1] V.Roudnev and B.D.Esry, Phys. Rev. Lett. 99, 220406 (2007) [Preview Abstract] |
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R1.00020: Multi-electron Effects in High-Order Harmonic Generation: Homonuclear vs. Heteronuclear Diatomic Molecules John Heslar, Shih-I Chu We present a \textit{self-interaction-free }time-dependent density-functional theory (TDDFT) with proper asymptotic \textit{long-range} potential for nonperturbative treatment of very-high-order nonlinear response of multi-electron molecular systems to intense laser fields. A time-dependent generalized pseudospectral method is developed in prolate spheroidal coordinate system for accurate solution of both the electronic structure and TDDFT equations for homonuclear and heteronuclear diatomic molecules. The theory is applied to a detailed \textit{all-electron} study of high-order harmonic generation (HHG) processes of CO, N$_{2}$, F$_{2}$, BF, and HF in intense laser fields. We found distinctive difference between the responses of homonuclear vs. heteronuclear diatomic molecules. First, while the homonuclear diatomics show only the odd harmonics, both even and odd harmonics are observed for heteronuclear diatomics. Second, destructive interference in HHG is observed in some MOs for homonuclear diatomics but not for heteronuclear diatomics. More detailed results will be presented in the conference. [Preview Abstract] |
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R1.00021: Orientation effects in high-order harmonic generation of H$_{2}^{+}$ subject to strong laser fields Dmitry A. Telnov, Shih-I Chu We present \textit{ab initio} 3D calculations of the orientation-dependent high-order harmonic generation (HHG) of the hydrogen molecular ion H$_{2}^{+}$ subject to intense linearly polarized laser pulses with the wavelength 800nm [1]. The nuclei are kept at the equilibrium separation of 2 a.u., and the initial electronic state can be either $1\sigma_{g}$ (ground) or $1\sigma_{u}$ (first excited) state. Split-operator technique in the energy represenation and generalized pseudospectral discretization in prolate spheroidal coordinates are used to solve the time-dependent Schr\"odinger equation. HHG power spectra show strong dependence on the orientation angle between the molecular axis and the polarization direction of the laser field. Particularly, orientation-selected resonances with other electronic states are well pronounced. Two-center interference effects in the HHG spectra are also analyzed.\\ 1. D. A. Telnov and S. I. Chu, Phys. Rev. A \textbf{76}, 043412 (2007). [Preview Abstract] |
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R1.00022: Time-Resolved Observation of Molecular Dissociation Using High Harmonic Generation Julien B. Bertrand, Hans Jakob W\"orner, Daniil Kartashov, David M. Villeneuve, Paul B. Corkum We have realized the first experiments towards dynamic orbital tomography by observing high harmonics generation from dissociating molecules. A pump pulse centered at 400 nm launches a dissociative wave packet in an electronically excited state and a delayed 800 nm pulse generates high harmonics from the excited sample. In a complementary experiment, the ion yield of the two-color experiment has been measured and the range of intensities corresponding to dominant single-photon excitation of the molecules has been identified. In both systems, excitation enhances ionization at short pump-probe delays but decreases the harmonic yield. The results obtained for the dissociation of Br2 and NO2 are compared and found to reveal characteristic details of two fundamentally different dissociation mechanisms. The requirements for dynamical orbital tomography are discussed. [Preview Abstract] |
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R1.00023: \textit{Ab initio} exploration of the frequency comb structure and coherence in high-order harmonics of multi-electron systems driven by a sequence of ultrashort laser pulses Juan J. Carrera, Shih-I Chu We present an \textit{ab initio }nonpertubative investigation of the frequency comb structure and coherence within each order of the high harmonic generation (HHG) of rare gas atoms by means of the self-interaction-free time dependent density functional theory (TDDFT). The time-dependent exchange-correlation potential is constructed by means of the time dependent optimized effective potential (TDOEP) method. The TDOEP equations are solved accurately and efficiently by means of the time-dependent generalized pseudospectral technique. We explore in detail the temporal coherence and robustness of the comb structure by varying the laser pulse duration $t$, the number of pulses $N$, and the laser intensity. We found that a nested comb structure appears within each order of the harmonics, ranging from the first harmonic all the way to the cut-off harmonic, and this global pattern persists regardless of the values of $t$ and $N$ used, and even in the presence of substantial ionization. [Preview Abstract] |
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R1.00024: SHORT PULSE (E.G., ATTOSECOND, FEMTOSECOND) PROCESSES |
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R1.00025: Intensity-dependent branching ratio of ND$^{+}$ dissociation in an intense laser field. J. McKenna, A.M. Sayler, B. Gaire, Nora G. Johnson, E. Parke, K.D. Carnes, B.D. Esry, I. Ben-Itzhak We investigate the fragmentation of an ND$^{+}$ molecular ion beam induced by intense femtosecond (40 fs) 795nm laser pulses. The individual dissociation channels (N$^{+}$ + D and N + D$^{+})$ of this astrophysically important molecule are uniquely separated by a coincidence measurement of the fragments. We observe that the branching ratio of the channels has a strong dependence on laser field strength over the intensity range 2x10$^{13}$ -- 3x10$^{15}$ W/cm$^{2}$. Additionally, using measurements of the kinetic energy release and angular distributions for these channels as a guide, we identify the most probable dissociation pathways. [Preview Abstract] |
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R1.00026: A comparative study of dissociation and ionization of isoelectronic N$_{2}^{+ }$and CO$^{+}$ molecular ions in an ultrafast intense laser field. B. Gaire, Nora G. Johnson, J. McKenna, A.M. Sayler, E. Parke, K.D. Carnes, B.D. Esry, I. Ben-Itzhak The response of the molecular ion beams N$_{2}^{+ }$and CO$^{+}$ to intense (up to 5$\times $10$^{15}$ W/cm$^{2})$ ultrashort laser pulses (10 and 45 fs) at 790 nm wavelength is investigated. For this purpose, we employ a coincidence 3D momentum imaging method to separate all breakup channels and then obtain kinetic energy release spectra and angular distributions of each of the channels. In particular, we will make a direct comparison between N$_{2}^{+}$ and CO$^{+}$ fragmentation focusing on the similarities and differences of these two molecules that share similar electronic configurations. The relative branching ratios of all the relevant breakup channels will also be discussed. [Preview Abstract] |
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R1.00027: Direct Coulomb explosion imaging of coherent rotational dynamics induced by few-cycle laser pulses in light and heavy hydrogen Irina Bocharova, Maia Magrakvelidze, Predrag Ranitovic, Dipanwita Ray, Lewis Cocke, Igor Litvinyuk We followed fast evolution of angular distributions for H$_{2}$ and D$_{2}$ molecules after their interaction with 8 fs 800 nm laser pulses. The rotating molecules were exploded by another few-cycle probe pulse time-delayed for up to 10 ps in respect to the pump. For neutral molecules we observed coherent rotational dynamics characterized by periodic revivals without noticeable decoherence within the 10 ps time-scale. For D$_{2}$ up to 4 rotational states were involved in the wavepackets for each of the two spin isomers. In light hydrogen the resulting dynamics was dominated by beating of just two rotational states. The experimental data are in excellent agreement with our numerical simulations obtained by solving time-dependent Schr\"{o}dinger equation. For molecules that were ionized by the pump pulse we observed both vibrational and rotational dynamics. Time-dependent angular distributions for the molecular ions exhibit transient alignment only soon after the pulse (20 fs for H$_{2}^{+}$ and 40 fs for D$_{2}^{+})$ with no consequent revivals within the next 10 ps. [Preview Abstract] |
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R1.00028: Enhanced carrier-envelope phase effect in photoexcitations of alkali atoms Fatima Anis, B.D. Esry A carrier-envelope phase (CEP) effect has recently been predicted in the photoexcitation of Cs $[1]$. Although interesting, the effect found in $[1]$ is unfortunately very weak and likely to be inaccessible to experimentalists. With the hope of finding a larger effect, we have performed a series of calculations for Li, Na, K, Rb, and Cs. Among these atoms, Na is the most promising candidate for CEP effect in photoexcitation. In particular, we found a strong modulation of about 80 percent in the excitation probability as a function of CEP for the 3p and 3d states at a peak intensity of about $8\times10^{12}$ W/cm$^2$. We have seen a modulation of more than five percent along with more than five percent population in many other states for these alkali atoms as well. The CEP effects are generally larger for Li and Na than for Rb and Cs. We hope that finding a bigger modulation in a strong signal will make it possible to observe the effect experimentally. \\ $[1]$ T. Nakajima and S. Watanabe, Phys. Rev. Lett. {\bf 96}, 213001 (2006). [Preview Abstract] |
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R1.00029: Dynamics of two-photon double ionization of helium in short intense XUV laser pulses Xiaoxu Guan, Klaus Bartschat, Barry Schneider We present an {\it ab-initio} non-perturbative time-dependent approach to the problem of a helium atom driven by an intense XUV laser pulse. Based on the finite-element discrete-variable-representation, a novel space discretization is proposed for the radial grid in spherical coordinates. Absolute angle-integrated and triple-differential cross sections for double ionization by absorption of two photons are obtained over a range of photon energies between 39.5$\,$eV (31.4$\,$nm) to 54$\,$eV (23$\,$nm), where the process is dominated by non\-sequential ionization mechanisms. We show that the agreement with several other sets of previous predictions is good, as long as the effective interaction time is defined properly. Two-photon double ionization at the photon energy of 57.0$\,$eV (22$\,$nm), for which both sequential and nonsequential channels are open, is also discussed. For double photo\-ionization in the near-threshold regime, our results do not indicate a preferential mode of energy sharing between the two escaping electrons, while asymmetric energy sharing becomes the dominant mode with increasing excess energy. Overall, the two ionized electrons strongly prefer to escape along the polarization axis of linearly polarized laser fields. [Preview Abstract] |
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R1.00030: Vortex Creation and Dynamics in Atoms by Short Electric Field Pulses. Teck-Ghee Lee, Serge Ovchinnikov, James Sternberg, Joe Macek, David Schultz We report the creation of vortex rings when an atom is exposed to very short electric field pulses. A full-dimensional time-dependent Schrodinger equation has been used to investigate the creation and the time-dependent dynamics of these vortex rings within the limit of weak and strong electric field intensities. The underlying conditions that control the vortex creation, collapse and survival are identified. We find that (i) the vortices can be created by both weak and strong electric fields, (ii) the number of vortices depends on the pulse duration and (iii) the vortex trajectories depend on the pulse intensities. Our study indicates that similar phenomena will occur for intense laser-atom interactions. [Preview Abstract] |
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R1.00031: Extracting the shake-up amplitudes from XUV-IR pump-probe experiments Stefan Nagele, Johannes Feist, Emil Persson, Joachim Burgd\"orfer The rapid progress in the creation of attosecond pulses opens the door to time-resolved control and observation of electronic motion in atoms. In a recent experiment, Uiberacker \emph{et~al.}~[1] exposed a gas of neon atoms to a phase-stabilized few-cycle IR laser pulse and a synchronized XUV subfemtosecond pulse. The XUV pulse directly ionizes one electron and excites a second electron through shake-up, which is then tunnel ionized by the IR field. By varying the time delay between the two pulses and measuring the double ionization yield, they were able to directly observe electron tunneling in the time domain. We will present numerical studies which suggest that with such a pump-probe setup it is possible to directly determine the shake-up amplitudes (both modulus and phase) of the electronic wave packet created by the XUV laser burst. Such information is not accessible in energy-domain measurements and thus represents a prime example for novel information gained from time-resolved attosecond spectroscopy.\\ $[1]$ M.~Uiberacker et al., \emph{Nature} \textbf{446}, 627 (2007). [Preview Abstract] |
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R1.00032: Femtosecond Electron Sources and Attosecond Electron Foci Shawn Hilbert, Amanda Fricke, Cornelis Uiterwaal, Herman Batelaan We report progress on a nanometer-sized femtosecond electron source. The source consists of an 80-MHz repetition rate femtosecond laser with a tungsten field emission tip. Our autocorrelation spectra support the claim$^{1}$ that the emission process is dependent on the electric field of the laser pulse. This field dependence suggests sub-cycle ($T_{\mbox{cycle}} =2\pi /\omega =2.7\mbox{ fs})$ electron emission.$^{1,2}$ Consistently, we found that the duration of the emission process has an upper bound of 100 fs.$^{3}$ However, we now deduce a lower bound for the emission process duration of about 10 fs. Nevertheless, this electron source may be combined with a temporal lens to focus the electron pulses to subcycle temporal widths.$^{4 }$ $^{1}$P. Hommelhoff, \textit{et} \textit{al}, Phys. Rev. Lett. 96, 077401 (2006) $^{2}$P. Hommelhoff, \textit{et} \textit{al}, Phys. Rev. Lett. 97, 247402 (2006) $^{3}$B. Barwick, \textit{et} \textit{al}, New J. Phys. 9, 142 (2007) $^{4}$P. Baum, A. H. Zewail, Proc. Natl. Acad. Sci. USA. 104, 18409 (2007) * This material is based upon the work supported by the National Science Foundation under Grant Nos. PHY-0355235 and PHY-0653182. [Preview Abstract] |
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R1.00033: Measuring the GVD of transparent solvents and creation of laser-etched holographic mirrors Timothy Scarborough, James Strohaber, Chad Petersen, Cornelis Uiterwaal We report experimental values of the group velocity dispersion (GVD) of water and methanol at 800 nm. These values were measured by sending 50-fs, 800-nm pulses with various amounts of chirp through a cell filled with a solution of fluorescein in these solvents and recording the production of visible 2-photon fluorescence light using a commercial digital camera. This simple setup also gives information on the duration of our pulses and has allowed us to identify behavior consistent with the presence of third-order spectral phase in the pulse. Additionally, we introduce a simple and practical method[1] to create ultrashort, intense optical vortices (`donut modes') for applications using high-intensity lasers. A laser-etching process is used to encode a holographic grating onto laser-quality gold mirrors, which can withstand intensities of up to $10^{12}\mbox{W/cm}^2$. With new methods for angular dispersion compensation[2], optical vortices can be produced with intensities $\sim 10^{11}\mbox{W/cm}^2$. [1] Strohaber J, Scarborough T, and Uiterwaal C J G J \textit{Appl. Opt.} \textbf{46} 8583 (2007) [2] Strohaber J, Petersen C, and Uiterwaal C J G J \textit{Opt. Lett.} \textbf{32} 2387 (2007) [Preview Abstract] |
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R1.00034: Rescattering in extended atomic systems Jan M. Rost, Ulf Saalmann Laser-driven rescattering of electrons is the basis of many strong-field phenomena in atoms and molecules. Here, we will show how this mechanism operates in extended atomic systems, giving rise to optimal energy absorption. Rescattering from extended systems can also lead to energy loss, which in its extreme form results in non-linear photo-association. Intense-laser interaction with clusters is discussed as an example. We explain fast electronic emission by rescattering of electrons at the highly charged cluster, using experimental and numerically obtained electron spectra. [Preview Abstract] |
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R1.00035: Coulomb Explosion of Transition Metal Oxides D.E. Blumling, S.G. Sayres, A.W. Castleman, Jr. Intense femtosecond pulses of light (624 nm) are employed to investigate the formation of high charge states and kinetic energy release (KER) from the Coulomb explosion of various transition metal oxide clusters. A molecular dynamics simulation is used to predict KER values for the ground state structures of the representative species as determined by density functional theory calculations. [Preview Abstract] |
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R1.00036: Large-angle electron diffraction structure in laser-induced rescattering from rare gases D. Ray, I. Bocharova, C. Maharjan, P. Ranitovic, B. Gramkow, M. Magrakvelidze, S. De, I.V. Litvinyuk, A.T. Le, C.D. Lin, C.L. Cocke, B. Ulrich, T. Morishita, G.G. Paulus We have measured full momentum images of electron rescatterred from Xe, Kr and Ar following the liberation of the electrons from these atoms by short, intense laser pulse. Structural study of transient target atoms (or molecules) can be done by focusing on the high energy backscattered electrons in such laser-matter interactions. Recent theoretical developments show that full solutions to time-dependant Schrodinger equation including rescatttering allow the identification of specific ``back rescattering ridges'' (BRR) along which the angular structure of the differential cross section is clearly visible and very target dependant. We have experimentally observed these predicted features in the momentum images. [Preview Abstract] |
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R1.00037: ULTRAFAST IONIZATION |
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R1.00038: Strong-Field Double Ionization of hydrogen: Wavelength Dependent Study Igor Litvinyuk, Dipanwita Ray, Daniel Comtois, Asad Hasan, David Villeneuve, Jean-Claude Kieffer, Ali Alnaser We studied double-ionization of H2 and D2 by intense femtosecond laser pulses of different wavelengths (500, 550, 600, 650, 800, 1300, 2000 nm) and peak intensities, by measuring kinetic energy release of resulting fragments. In addition to fragments from the well known enhanced ionization channel (5-6 eV), higher energy protons/deuterons (8-10 eV) were for the first time observed when using shorter wavelengths (500-650 nm) at high-peak intensities. This channel exhibited wavelength dependence, with KER decreasing for longer wavelengths. The channel was observed with both linear and circular polarization. We attribute this phenomenon to 3-photon excitation of molecular ion sequentially followed by the second ionization. [Preview Abstract] |
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R1.00039: Attosecond light pulse induced photo-association Jan M. Rost, Paula Riviere, Camilo Ruiz We explore stimulated photo-association in the context of attosecond pump-probe schemes of atomic matter. An attosecond pulse -- the probe -- is used to induce photo-association of an electronic wave packet which had been created before, typically with an attosecond pump pulse at an atomic center different from the one of photo-association. We will show that the electron absorption is maximal for a certain delay between the pulses. Two ways of enhancing and controlling stimulated photo-association are proposed, namely using an additional infrared pulse to steer the electronic wave packet and using a train of attosecond pulses instead of a single pair. A direct application of ultrafast stimulated photo-association is the measurement of atomic distances. [Preview Abstract] |
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R1.00040: Towards femtosecond time-resolved XUV photoionization studies of Helium nanodroplets Oliver Gessner, Oleg Kornilov, Chia Wang, Andrew Healy, Mathew Leonard, Chunte Peng, Stephen Leone, Daniel Neumark Helium II nanodroplets constitute a unique cryogenic matrix for the creation, isolation and spectroscopy of regular and exotic species, such as free radicals and molecules in high-spin states. The droplets readily pick up atoms and molecules but interact only very weakly with the respective dopants due to their superfluid nature. We are currently setting up a high-order harmonic generation-based femtosecond XUV-pump, IR-probe experiment to study the photoionization dynamics of pure and doped Helium nanodroplets close to the atomic Helium IP (24.6 eV) in real-time. Using Velocity-Map Imaging (VMI) photoelectron spectroscopy we will monitor the photoionization dynamics of the droplets, of the dopants in the droplet environment, and the charge- and energy-transfer mechanisms between droplets and dopants. [Preview Abstract] |
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R1.00041: COLLISIONS INVOLVING ANTIMATTER |
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R1.00042: Absolute cross section for positron impact ionization of hydrogen near threshold S.J. Ward, Krista Jansen, Janine Shertzer, J.H. Macek The hyperspherical hidden crossing method (HHCM) is used to
investigate
positron impact ionization of hydrogen near threshold. In this
quantum
calculation, the adiabatic Hamiltonian for arbitrary $L$ is
expanded about the
Wannier saddle point. The lowest order equation is solved
analytically for
the adiabatic eigenvalue; we use first and second order
perturbation theory
to calculate correction terms. We show that the Wannier threshold
law and
the extended threshold law are independent of $L. $We calculate
absolute positron
impact ionization cross sections for partial waves $L=0, 1, 2, 3$
in the energy range $0 |
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R1.00043: Cross sections for antiproton collisions Alejandro Saenz, Armin Luehr The presently constructed large facility FLAIR at the GSI Darmstadt (Germany) will give new impetus to low-energy antiproton physics and their use for fundamental physics like tests of the CPT-invariance or gravity of antimatter. The envisaged energies will allow investigations of antiproton collisions below the applicability of the first Born approximation. This leads to an increased interest in theoretical investigations of slow antiproton collisions. The theoretical cross-sections should in turn also be useful for the design of the new experimental facility where, e.g., the interaction of antiprotons with residual-gas atoms is important. Theoretical investigations for collisions of the alkali metal atoms Li, Na and K with antiprotons in an energy range from 0.2 to 1000 keV have been performed. Cross sections for excitation, ionization, and angular resolved ionization are presented. The calculations are based on a time-dependent close coupling method based on the classical trajectory approximation. The approach is currently extended from atomic to molecular targets. [Preview Abstract] |
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R1.00044: Resonances in PsH below the p+Ps$^-$ threshold Zong-Chao Yan, Y.K. Ho Recently, Di Rienzi and Drachman carried out an investigation of high-lying resonances in the Ps-H system lying below the Ps$^-$ + H$^+$ threshold~[1]. Using an effective potential formalism, they calculated the resonance energies for some S, P and D states. In the present work, we present a calculation of S-wave resonances lying below the p + Ps$^-$ threshold by using the method of complex-coordinate rotation~[2]. We use elaborate Hylleraas wave functions~[3] in which all the six inter-particle coordinates are included~[4]. Using up to 6412 terms in the basis functions, resonance energies and widths for several lower members of a Rydberg series are calculated. At the meeting, we will compare our preliminary results with those of the earlier calculation~[1]. \newline [1] J. Di Rienzi and R. J. Drachman, Phys. Rev. A 76 (2007) 032705. \newline [2] Y. K. Ho, Phys. Rept. 99 (1983) 1, and references therein. \newline [3] Z.-C. Yan and Y. K. Ho, Phys. Rev. A 59 (1999) 2697. \newline [4] Z.-C. Yan and G. W. F. Drake, J. Phys. B. 30 (1997) 4723. [Preview Abstract] |
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R1.00045: Positron-atom scattering using pseudo-state energy shifts Jim Mitroy, Jun-Yi Zhang, Michael Bromley, Scott Young A simple way to generate low-energy phase shifts for elastic scattering using bound-state calculations is applied to the problem of $e^+$-Mg and $e^+$-Zn scattering. The method uses the energy shift between a small reference calculation and the largest possible configuration interaction calculation of the lowest energy pseudo-state/s as the input to tune a semi-empirical optical potential. The $s$- and $p$-wave phase shifts up to the first excitation threshold are given for both systems. The $e^+$-Mg cross section has a prominent $p$-wave shape resonance at an energy of about 0.0094 eV with a width of 0.0108 eV. The cross section maxima is about 4800 $a_0^3$, while the $Z_{\rm eff}$ achieves a value of 1300 at an energy of 0.108 eV. [Preview Abstract] |
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R1.00046: Positron transport in low pressure argon Joan Marler, Z.Lj. Petrovi\'c, M. \v{S}uvakov, G. Malovi\'c, S.J. Buckman, R.E. Robson Motivated by an increasing number of applications, new techniques in the analysis of electron transport have been developed over the past 30 years or so, but similar methods had yet to be applied to positrons. We present the first in-depth look at positron transport in pure argon gas using a recently established comprehensive set of cross sections and well-established Monte-Carlo simulations. The behavior of positrons can be markedly different from electrons, e.g., a positron swarm can appear to move only slowly away from the positive electrode even though the average velocity may be considerable. This may be understood by realizing that Ps formation in argon has a comparatively large, strongly energy-dependent cross section and significantly retards the centre-of-mass motion of the swarm. From an experimental point of view, positron swarms may be the best place to look for theoretically predicted non-conservative effects on transport phenomena. [Preview Abstract] |
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R1.00047: Positron Scattering from 3-hydroxy-tetrahydrofuran Michael Brunger, Antonio Zecca, Luca Chiari, Anindya Sarkar We report results from the first measurements of total cross sections for positron scattering from the inportant bio-molecule 3-hydroxy-tetrahydrofuran. In this case the energy range of our work is 0.4 -- 40.4 eV. While there are currently no theoretical data against which we can compare these results, a comparison with corresponding measurements for the geometrically similar species tetrahydrofuran$^1$ is made.\vskip 0.5cm \noindent $^1$A Zecca, C Perazzolli and M J Brunger 2005 J Phys B $\underline{\rm 38}$, 2079. [Preview Abstract] |
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R1.00048: Positron transport and thermalization in low pressure molecular gases A. Bankovi\'c, Z.Lj. Petrovi\'c, M. \v{S}uvakov, S. Dujko, G. Malovi\'c, J.P. Marler, R.D. White We present calculations of transport coefficients and thermalization times for positrons in H$_2$, N$_2$ and CF$_4$ that are relevant for modeling of the Surko trap and aid in the interpretation of transport and annihilation experiments in low pressure gases. Recently it became possible to compile comprehensive cross section sets for these gases. The key novelty as compared to electron transport is the effect of positronium formation which changes the number of particles and has a strong energy dependence. This coupled with spatial separation by energy of the positron swarms leads to counter intuitive behaviour of some of the transport coefficients which may explain experimental observations in buffer gas traps. The relative magnitude of positronium formation to electronic excitations and the relative positions of their thresholds control both non-conservative transport phenomena and the efficiency of thermalization. The effect of vibrational excitation on low energy positrons is also considered. [Preview Abstract] |
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R1.00049: Role of inelastic escape channels in Feshbach-resonant positron annihilation J.A. Young, C.M. Surko Energy-resolved positron-molecule annihilation spectra show that positrons can bind to molecules via the vibrational Feshbach resonance (VFR) mechanism [1,2]. Here we take a closer look at VFR in large molecules, paralleling the talk by J. A. Young (this meeting). After normalizing out a weak dependence on binding energy, the magnitudes of C-H stretch mode resonances in large hydrocarbons obey a power-law scaling with the number of vibrational degrees of freedom [3]. The only known outliers are partially fluoronated alkanes. New results are presented for these molecules showing that this behavior can be explained by a strong inelastic channel. For ordinary alkanes, we show that annihilation data taken using 300~K thermal positrons is quantitatively consistent with data taken at higher positron energies. The role played by intramolecular vibrational relaxation (IVR) will also be discussed. \\ ~[1] L. D. Barnes, J. A. Young, and C. M. Surko, \textit{Phys. Rev. A} {\bf 74}, 012706 (2006). \\ ~[2] G. F. Gribakin and C. M. R. Lee, \textit{Phys. Rev. Lett.} {\bf 97}, 193201 (2006). \\ ~[3] J. A. Young and C. M. Surko, \textit{Phys. Rev. Lett.} {\bf 99}, 133201 (2007). [Preview Abstract] |
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R1.00050: Resonant structures in the positron annihilation spectra of small molecules C.M. Surko, J.A. Young Energy-resolved measurements of positron-molecule annihilation show that positrons can attach to molecules via vibrational Feshbach resonances (VFR) [1]. Furthermore, thanks to a recent theory by Gribakin and Lee, it is possible to quantitatively predict the positron-molecule annihilation spectra for small molecules in which all the vibrational modes are infrared-active [2]. In this paper, we examine the annihilation spectra for a variety of small molecules and relate them to this theory. We find that fundamental-mode \emph{and} multi-mode VFR are necessary to explain the spectra of molecules such as methanol. We also present results for molecules such as water and CO$_2$ that do not have clearly identifiable VFR but appear to have structure to their spectra. \newline ~[1] L. D. Barnes, J. A. Young, and C. M. Surko, \textit{Phys. Rev. A} {\bf 74}, 012706 (2006). \newline ~[2] G. F. Gribakin and C. M. R. Lee, \textit{Phys. Rev. Lett.} {\bf 97}, 193201 (2006). [Preview Abstract] |
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R1.00051: Convergence and Momentum Dependence of the Correlation Correction to the Amplitude of Positron Annihilation on Atoms Gleb Gribakin, Brendan McGrath Positron annihilation rates in solids and in gases are strongly affected by electron-positron correlations. Observed rates exceed those evaluated in the independent-particle approximation many times. In solids this effect is usually taken into account through an enhancement factor (EF), which depends on the electron density [1]. Correlations also affect the momentum distribution of the annihilating electron-positron pairs, which determines the shape of the annihilation gamma spectrum. This effect is beyond the EF approximation and is often neglected [1]. Using a many-body theory framework [2] we analyse the convergence of the 1st-order correction to the annihilation amplitude with the orbital angular momentum $l$ of the intermediate electron and positron states. We find that these contributions converge as $(l+1/2)^{-2}$, and have a distinctly different momentum dependence compared with the 0th-order amplitude, narrowing the annihilation spectra. \begin{enumerate}\setlength{\itemsep}{-3pt}\setlength{\itemindent}{-12pt} \item M. Alatalo et al., Phys. Rev. B {\bf 54}, 2397 (1996). \item G. F. Gribakin and J. Ludlow, J. Phys. B {\bf 35}, 339 (2002); L. Dunlop and G. F. Gribakin, {\em ibid.} {\bf 39}, 1647 (2006). \end{enumerate} [Preview Abstract] |
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R1.00052: ION-ATOM AND ION-ION COLLISIONS |
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R1.00053: Charge exchange in $H^+ + He^+$ collision Nicolais Guevara Leon, John R. Sabin, Erik Deumens, Yngve Ohrn Charge exchange in $H^+ + He^+$ collision are investigated theoretically at projectile energies below the ionization threshold at about $100$ keV/amu. The electron nuclear dynamics (END) method is used to analyze the collision processes. Total charge exchange cross sections were calculated and compared with other theoretical and experimental data. [Preview Abstract] |
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R1.00054: Double ionization of helium by ion impact assessed using four-body Dalitz plots Marcelo Ciappina, Michael Schulz, Tom Kirchner, Daniel Fischer, Robert Moshammer, Joachim Ullrich We have performed experimental and theoretical studies of double ionization (DI) of helium by 6 MeV proton impact using a recently developed tool: four-particle Dalitz plots.\footnote{M. Schulz \textit{et al}, J. Phys. \underline {B22}, 3091 (2007)} These plots are basically an extension of conventional Dalitz plots originally introduced in particle physics to analyze three-body fragmentation processes. DI represents a \textit{four-body} fragmentation process and consequently an extra dimension needs to be incorporated. Four-particle Dalitz plots are very powerful because they enable the representation of multiple differential cross sections as a function of all four fragments in a single spectrum without loss of any part of the total cross section. As a result, the relative importance of the various interactions between the fragments can be studied in great detail. Our results suggest that an uncorrelated DI mechanism, involving two independent interactions of the projectile with both electrons, is significantly more important than previously expected for such fast collisions. [Preview Abstract] |
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R1.00055: Electron Capture in Collisions between Protons and Hydrogen Atoms Thomas Winter Cross sections are being determined for electron transfer and other processes in intermediate (keV)- energy $p$-H collisions using a double-center Sturmian basis, substantially expanding pioneering Sturmian calculations carried out thirty years ago.\footnote{R.Shakeshaft, J. Phys. B {\bf 8}, 1114 (1975); Phys. Rev. A {\bf 18}, 1930 (1978).} The computer code for arbitrary nuclear charges, recently applied to $\alpha$-H collisons, \footnote {T.G. Winter, Phys. Rev. A {\bf 76}, 062702 (2007).} is being specialized to the homonuclear case to reduce the number of distinct matrix elements and the number of coupled channels. The results may be compared with large basis, double-center Gaussian results\footnote{N. Toshima, Phys. Rev. A {\bf 59}, 1981 (1999).}; triple-center results\footnote{T. G. Winter and C.D. Lin, Phys. Rev. A {\bf 29}, 567 (1984).}; double-center, even-tempered basis results\footnote{J. Kuang and C. D. Lin, J. Phys. B {\bf 29}, 1207 (1996).}; other theoretical results; and numerous experimental results.\footnote{See T. G. Winter, Adv. At., Mol., Opt. Phys. {\bf 52}, 391 (2005).} [Preview Abstract] |
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R1.00056: Significance of Different Interactions in Transfer-Excitation A.L. Harris, M. Schulz, J.L. Peacher, D.H. Madison In the transfer-excitation process for proton-helium scattering, an incident proton captures one electron from a helium atom, and the remaining electron is left in an excited bound state of the helium ion. Theoretical fully differential cross sections (FDCS) will be compared with experimental results for this process. The theoretical approach used is a full four-body approach, taking each particle into account. This results in a T-matrix requiring a nine dimensional integral, which is numerically intensive. On the other hand, one of the great strengths of this approach lies in the fact that we have complete flexibility in the choice of wavefunctions, which provides the opportunity to examine the effects of different types of interactions. A fully correlated Hylleraas wavefunction is used for the initial state helium atom, and hydrogenic wavefunctions are used for the hydrogen atom and the residual ion in the final state. The focus will be on the role of projectile interactions for transfer-excitation. [Preview Abstract] |
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R1.00057: A Novel Merged-Beams Apparatus for Studying Anion-Neutral Reactions D.W. Savin, H. Bruhns, H. Kreckel, M. Lestinsky, W. Mitthumsiri, M. Schnell, B. Seredyuk, M.E. Bannister, C.C. Havener, A. Dorn, O. Heber, M.L. Rappaport, A.M. Covington We are developing a novel apparatus at the Columbia Astrophysics Laboratory to study anion-neutral reactions. Beginning with an anion beam, we use photodetachment to generate a self-merged, anion-neutral beams arrangement. Laboratory beam energies are in the keV range. Because the beams run co-linear, center-of-mass energies from the meV to keV range will be achievable. Our proof-of-principle measurement is the associative detachment (AD) reaction ${\rm H}^- + {\rm H} \to {\rm H}_2 + {\rm e}^-$. Published values for this process differ by over a factor of 5. Measurements using our novel apparatus will help to resolve this fundamental issue in physics and chemistry. We will observe the AD reaction by detecting fast H$_2^+$ ions formed through ionizing collisions of the AD-generated H$_2$ with the background gas in the vacuum chamber. Here we present the current status of the project and discuss our future plans. [Preview Abstract] |
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R1.00058: Creation, propagation and destruction of vortices in single atom wave functions for ion-atom collisions James Sternberg, J.H. Macek, Serge Ovchinnikov, Teck-Ghee Lee, D.R. Schultz Vortices are a nearly ubiquitous feature of nature. It is well known that they form in large scale processes such as weather, but they are also formed in the quantum realm. One place where they can be seen quite clearly is in the wave functions for ion- atom collisions at a set impact parameter. In this work we use a very low noise and highly accurate numerical method to propagate the time dependent Schr\"odinger equation (TDSE) for such a collision. With this method we see the formation of vortices in the wave function, the interaction between them and their destruction. We also observe how the transport of angular momentum by vortices affects the overall behavior of the wave function. [Preview Abstract] |
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R1.00059: Polarization of X-rays produced in charge-exchange collisions in astrophysical plasmas Marko Gacesa, Vasili Kharchenko, Robin C\^ot\'e The discovery of X-ray emissions from comets is important for solar system and astrophysical applications. It is believed that the underlying mechanism are charge-exchange collisions between the highly charged solar wind ions and the atoms and molecules present in the cometary and planetary atmospheres as well as in the interstellar gas. We describe a simple charge-exchange process of the form $A^{q+} + B \rightarrow A^{(q-1)+*} + B^{+}$ and predict the spatial distribution of emitted X-rays and their polarizations by solving Schroedinger equation in quasi-molecular orbital approach. [Preview Abstract] |
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R1.00060: COLLISIONS INVOLVING CLUSTERS |
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R1.00061: Influence of Structure and Charge State on the Mechanism of CO Oxidation on Gold Clusters Grant Johnson, Christian Burgel, Nelly Reilly, Roland Mitric, Michele Kimble, Eric Tyo, A.W. Castleman, Vlasta Bonacic-Koutecky Gas-phase reactivity experiments and high level theoretical calculations have been employed to study the interaction of both positively and negatively charged gold oxide clusters with carbon monoxide (CO). We demonstrate that for negatively charged clusters CO is oxidized to CO$_{2}$ by an Eley-Ridel-like (ER-) mechanism involving the attack of CO on oxygen rather than gold. In contrast, for positively charged clusters, the oxidation reaction may also occur by a Langmuir-Hinshelwood-like (LH-) mechanism involving the initial binding of CO to a gold atom followed by subsequent migration to an oxygen site. The LH mechanism is made possible through the large energy gain associated with the adsorption of two CO molecules onto cationic gold clusters. Structure-reactivity relationships are also established which demonstrate that terminally bound oxygen atoms are the most active sites for CO oxidation. Bridge bonded oxygen atoms and molecularly bound O$_{2}$ units are shown to be inert. We also establish an inverse relationship between the binding energy of CO to gold clusters and the energy of the clusters lowest unoccupied molecular orbital (LUMO). [Preview Abstract] |
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R1.00062: COLLISIONS INVOLVING SURFACES |
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R1.00063: Resonant neutralization of hydrogen anions near the Be(0001) surface Nathan Brown, Himadri Chakraborty, Uwe Thumm The resonant charge transfer interaction between atomic ions and metal surfaces is a tool to examine the surface electronic structure and its associated implications to the surface chemistry. Using a Crank-Nicholson propagation technique we simulate and visualize the dynamical electron distribution during a charge transfer reaction of a hydrogen anion with a plane Be (0001) surface. The time-dependent information as the ion evolves, that is, as it decays and captures, is obtained and the final ion survival probability is determined. Comparisons with previous results involving Cu and Pd surfaces [1] uncover the dependence of the ion survival on the size, position and detailed structure of the surface electronic band gap. [1] Chakraborty et al., \textit{Nucl. Instrum. Meth.} B \textbf{241}, 43 (2005) [Preview Abstract] |
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R1.00064: QUANTUM AND/OR NONLINEAR OPTICS |
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R1.00065: Cold Atoms inside a Hollow Core Photonic Crystal Fiber Sebastian Hofferberth, Michal Bajcsy, Vlatko Balic, Thibault Peyronel, Alexander Zibrov, Vladan Vuletic, Mikhail Lukin Cold atoms confined inside a hollow core photonic crystal fiber are a promising medium for studying nonlinear optical interactions at extremely low light levels. Confinement of both atoms and photons inside the fiber core to a diameter of just a few wavelengths results in high electric field intensity per photon and large optical depths with a relatively small number of atoms. Additionally, the interaction length of atoms and photons is not limited by diffraction. We describe recent progress in our experiment that uses a combination of magnetic trapping and a red-detuned optical dipole trap to load cold Rb87 atoms into the hollow-core fiber. We present a detailed study of the loading process and characterization of the atomic ensemble in the fiber. Recent results of few photon nonlinear optics experiments are also discussed. [Preview Abstract] |
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R1.00066: Quantum plasmonics: a nanoscale interface between photons and atoms Alexey Akimov, Aryesh Mukherjee, Chun Yu, Darrick Chang, Frank Koppens, Alexander Zibrov, Philip Zibrov, Hongkun Park, Mikhail Lukin We discuss recent theoretical and experimental developments towards a new, broadband approach for engineering photon-emitter interactions via subwavelength confinement of optical fields near metallic nanostructures. The tight confinement of guided excitations in these nanostructures, known as ``surface plasmons'', results in large interactions between single photons and single optical emitters without the use of a cavity, which can further be manipulated using quantum optical techniques. We report on recent experimental work demonstrating strong coupling between an individual CdSe quantum dot and a single surface plasmon in a proximal nanowire. Prospects towards single-photon nonlinear optics in such systems and robust, nanoscale atomic traps using surface plasmons are also discussed. [Preview Abstract] |
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R1.00067: Generation of strongly correlated photons in a nonlinear one-dimensional system Mohammad Hafezi, Darrick E. Chang, Vladimir Gritsev, Eugene Demler, Mikhail D. Lukin We present a theoretical investigation of a photonic system obeying the quantum non-linear Schr\"odinger equation in a finite size system. Such systems are now being implemented using a hollow-core fiber loaded with trapped alkali atoms. The tight transverse confinement of the photonic modes enables a large atom-field coupling strength. We investigate the effects of large nonlinearity on quantum correlations of transmitted and reflected photons. The widely tunable nonlinearity in the system enables one to coherently control statistical properties of photon fields and to create photonic Luttinger liquids. [Preview Abstract] |
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R1.00068: Novel systems for single-photon generation using quantum memory Philip Walther, Alex Nemiroski, Mason Klein, David Patterson, Alexey Gorshkov, Sahand Hormoz, Alexander Zibrov, Ronald Walsworth, John Doyle, Mikhail Lukin The effective generation of single photons on demand is one of the most important prerequisites for scalable quantum computation and quantum communication using linear optics and measurement-induced nonlinearities. Using atomic memories and the controlled interaction of photons and atoms could allow for the realization of such single-photon sources. One promising approach is based on writing and reading single excitations in atomic ensembles using Raman processes and electromagnetically induced transparency. We report on the development of two novel experimental systems for the realization of such single-photon sources, each combining long coherence times with high efficiencies and purity. The first approach makes use of 1mm-wide paraffin-coated Rubidium cells at room temperature whose volumes are in the order of the interaction region. The second approach makes use of buffer gas cooling to create an appropriate dense medium with excellent coherence properties. Experimental realization and comparison of these two approaches will be presented. [Preview Abstract] |
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R1.00069: Joint CPT and N resonance in compact atomic time standards Michael Crescimanno, Michael Hohensee, Yanhong Xiao, David Phillips, Ron Walsworth Currently development efforts towards small, low power atomic time standards use current-modulated VCSELs to generate phase-coherent optical sidebands that interrogate the hyperfine structure of alkali atoms such as rubidium. We describe and use a modified four-level quantum optics model to study the optimal operating regime of the joint CPT- and N-resonance clock. Resonant and non-resonant light shifts as well as modulation comb detuning effects play a key role in determining the optimal operating point of such clocks. We further show that our model is in good agreement with experimental tests performed using Rb-87 vapor cells. [Preview Abstract] |
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R1.00070: Noise processes in Electromagnetically Induced Transparency Yanhong Xiao, Tun Wang, Susanne F. Yelin, Maria Baryakhtar, David F. Phillips, Ronald L. 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, magnetometers and stored light. We present experimental and theoretical study of EIT noise spectra and correlations in a Rb vapor cell. Applications of these results in atomic clocks, magnetometry, quantum optics, sensing and imaging are discussed. [Preview Abstract] |
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R1.00071: All-optical control of quantum state singlet-triplet character by Autler-Townes splitting. Omer Salihoglu, Peng Qi, Sonja Ingram, Ergin Ahmed, Marjatta Lyyra Using a four level extended Lambda excitation scheme [1] in $^{7}$Li$_{2}$, we have demonstrated that Autler --Townes splitting can be used to modify the mixing coefficients and thus the amount of singlet or triplet character of a pair of rovibrational A$^{1}\Sigma _{u}^{+}$ and b$^{3}\Pi _{u }$states perturbed by the spin-orbit interaction. The singlet triplet pair of levels is naturally separated by an energy gap of 600 MHz. As indicated earlier [2] such control of molecular valence electron spin polarization can be used to create new gateway levels to the dark manifold of triplet states in molecular systems with a singlet ground state in which the spin orbit interaction is very weak and only a few gateway levels to triplet states exist naturally. In addition, a direct measurement of the spin-orbit interaction strength is possible from the observed AT splitting lineshape [2]. \begin{enumerate} \item E. Ahmed et al., J. Chem. Phys. 124, 084308 --1 to 13 (2006). \item T. Kirova and F. C. Spano, Phys. Rev. A, 71, 063816 (2005). \end{enumerate} [Preview Abstract] |
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R1.00072: Collective excitation of surface plasmons by a linear dipole array J\'er\'emie Choquette, Karl-Peter Marzlin, 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. Optical dipoles placed near the metal interface have their radiative properties significantly affected by the presence of surface plasmon modes. The spontaneous emission rate is heavily modified and an optical emitter can decay both radiatively and into a surface plasmon. We consider a linear (pencil-like) arrangement of $N$ dipoles in vacuum near a metal film on the surface of a prism. In free space this arrangement would predominantly emit radiation along the axis of this pencil with an intensity that increases like $N^2$. We show that this gain persists in the presence of the metal film and an additional enhancement of the intensity can be achieved by the narrow characteristic of the radiation field emitted by the induced surface plasmon modes. This effect is rather insensitive to the alignment of the pencil due to the evanescent nature of surface plasmon fields. [Preview Abstract] |
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R1.00073: Giant Optical Nonlinearities Between Two Matched Pulses Andrew MacRae, Geoff Campbell, Zeng-Bin Wang, Karl-Peter Marzlin, Alexander Lvovsky One of the primary limitations of nonlinear optics is that relatively high intensities are needed to produce a noticeable effect. However, in an atomic system with electromagnetically induced transparency (EIT) it is possible to observe nonlinearities at light levels as low as a few photons per atomic cross section [1]. Implementation of the EIT-based nonlinearity with pulsed light may however be challenging as it requires the interacting pulses to propagate at equal group velocities. Recently, a scheme satisfying this requirement was proposed which employs double EIT in atomic Rubidium-87 [2]. We report on our recent progress towards experimentally realizing this scheme. We have successfully demonstrated a double EIT system in which two separate pulses may be simultaneously slowed or stored. By applying a large, homogenous magnetic field across the atomic vapor, thus splitting the atomic levels, we create a large nonlinear interaction in the form of XPM. *References: [1]: H. Schmidt, and V. Imamo\v{g}lu, Optics Letters 21 23 1996 [2]: Z.B. Wang, K.P. Marzlin, B.C. Sanders, Phys. Rev. Lett. 97 06, 2006 [Preview Abstract] |
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R1.00074: Four-wave mixing in a diamond configuration: correlated photons. R.T. Willis, F.E. Becerra, S.L. Rolston, L.A. Orozco We are investigating the use of spontaneous four-wave mixing in atomic vapors for the production of photon pairs of different wavelengths with non-classical correlations. We use a diamond atomic configuration with one ground, two intermediate, and one upper state. We observe stimulated four-wave mixing in both a vapor cell and a magneto-optical trap of Rb, producing light at 1367 nm with input beams of 780, 795, and 1324 nm. We will present our progress toward the measurement of the cross-correlation function between phase-matched, spontaneously emitted 780 and 1367 nm photons, with input beams of 795 and 1324 nm. [Preview Abstract] |
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R1.00075: Nonlinear beam shaping in an anisotropic magneto-optical trap Joel Greenberg, Marcos Oria, Daniel Gauthier We report on nonlinear beam shaping obtained in an anisotropic magneto-optical trap (MOT). In the anisotropic MOT, atoms are cooled in all directions but only trapped in the radial direction, thus producing a pencil-shaped volume of cold atoms. This sub-Doppler cooled collection of atoms can be made several centimeters long with optical depths (OD; Iout/Iin=exp(-OD)) on the order of 50, and has an approximately Gaussian radial density distribution. This allows for the observation of beam shaping in the regime where the medium must be considered as optically thick and diffraction during the interaction must be considered. [Preview Abstract] |
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R1.00076: Density Matrix Descriptions for Pump-Probe Optical Phenomena in Moving Atomic Systems Verne Jacobs Reduced density matrix descriptions are developed for pump-probe optical phenomena in moving many-electron atomic systems, taking into account atomic collisions and external magnetic fields. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. In a semiclassical perturbative treatment of the electromagnetic interaction, compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors. These expressions are valid for coherent atomic excitations and for the full tetradic-matrix form of the collision operator in the Markov approximation. [Preview Abstract] |
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R1.00077: Highly Directional Emission from Inhomogeneous Dielectric Microcavities G. Painchaud-April, J. Poirier, S. Saidi, Y.-A. Peter, E. Brasselet, L.J. Dub{\'e} We propose a novel method of extracting light beams from 2D microcavities. The concept is based on \textit{inhomogeneous dielectric cavities} (IDC) where the inhomogeneities arise from a space-dependent refractive index whose variations may be continuous (e.g. a localized induced gaussian profile of the index) or discontinuous (e.g. holes or refractive steps in the cavity material). Instead of smooth deformations of a circular cavity that produce directional output while sacrificing the quality factor Q, we intend to operate with an integrable geometry (a disk) and induce directionality through the (possibly reconfigurable) medium while preserving a high Q. The systems are interesting on two counts. Firstly, as classical objects, the IDC are equivalent to dielectric billiards (i.e. photonic escape is possible) where the broken symmetry of the material can induce a transition from regular to chaotic dynamics: chaos in an integrable billiard geometry. Secondly, guided by the classical phase space information, the wave dynamics can be ``engineered'' to produce highly directional emission with tailored optical properties, the grail of microcavity research. We have studied a number of configurations and will present results on their respective performances. [Preview Abstract] |
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R1.00078: Transport Mechanisms in Dielectric Optical Microcavities G. Painchaud-April, J. Poirier, L.J. Dub{\'e} Optical 2D microcavities have become a source of promising new technologies over the last decades. Applications ranging from high accuracy spectrometry to laser design will benefit from the development of such devices. The versatility of the concept resides in the ray-wave correspondence [1, 2]: the short wavelength limit of the system exhibits properties of well-known billiard systems, which may include Hamiltonian chaos. Therefore, since the wave behaviour of an optical microcavity is influenced by the underlying phase-space structure, a study and characterization of this structure becomes important to predict where the electromagnetic energy will flow out of the cavity. Whereas the correspondence works reasonably well for regular (classically integrable) and completely chaotic systems, partially chaotic systems of mixed phase space show transport properties largely influenced by tunnelling and localization effects with the consequence that the correspondence is all but lost. We will present the results of our investigations, in the ray and wave dynamics, in order to shed some light on the collaborating influence of the different transport mechanisms. [1] H. G. L. Schwefel et al., J. Opt. Soc. Am. \textbf{B21,} 923--934 (2004). [2] J. Wiersig and M. Hentschel, Phys. Rev. Lett, \textbf{100, }033901 (2008). [Preview Abstract] |
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R1.00079: Single Photon Nonlinearity in Cold Polar Molecular Arrays: Controlled Phase Operation T. Bragdon, R.M. Rajapakse, A.M. Rey, S.F. Yelin As a potential application of single photon nonlinearities in cold polar molecules, we present a schema for controlled phase operation in quantum computation. We compare decoherence vs. gate times with previous work on site addressed molecular qubits as a function of lattice density. We propose coherent control via protected many-body symmetric manifold. [Preview Abstract] |
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R1.00080: SLOWING AND STOPPING LIGHT |
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R1.00081: Electromagnetically Induced Transparency in Buffer-gas-cooled Rb Vapor Tao Hong, David Patterson, Alexey Gorshkov, Alexander Zibrov, Mikhail D. Lukin, John Doyle, Mara Prentiss We demonstrate a novel experimental system for coherent quantum and nonlinear optics. Using ~a He buffer gas to cool Rb vapor to 4.2 K produces an atomic sample with an optical depth (OD) exceeding 70 that supports electromagnetically induced transparency (EIT) with transmission as high 50{\%}, allowing us to systematically study EIT at large optical depths. We find that the two-photon EIT resonance that is a single peak at low optical depths splits into several peaks as the optical depth increases above 20. Detailed theoretical modeling indicates that the splitting is due to four wave mixing. Finally, we report the observation of slow pulse propagation with pulse delays of ~10 $\mu $s -- exceeding three times the input pulse width. [Preview Abstract] |
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R1.00082: Optimization of light storage for arbitrarily shaped pulses in atomic vapor Nathaniel Phillips, Irina Novikova, Alexey Gorshkov Efficient and reliable quantum communication will require the control of individual photons. As a step toward this objective, we have demonstrated promising techniques that involve using a dynamic form of electromagnetically induced transparency to optimally and reversibly map arbitrary pulse shapes of light onto an ensemble of warm Rubidium atoms. One technique employs time- reversal to determine, using an iterative procedure, the optimally-stored signal field for a given control field. Another method makes use of the one-to-one mapping between the decayless spin modes of the atoms and the signal field to calculate the optimal control field. We observe a good agreement with the theoretical predictions for lower optical depth ($< 15$). We also analyze possible effects responsible for the reduced storage efficiency at high optical depth, such as resonant four-wave mixing, ac-Stark shifts, etc. [Preview Abstract] |
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R1.00083: Raman Self-Focusing and Soliton Propagation in an Atomic Vapor Jonathan Green, Nicholas Proite, Brett Unks, Deniz Yavuz We analyze the theory behind Raman soliton propagation and soliton interactions in an atomic medium and discuss recent related experimental results. We use two strong lasers to drive a Raman transition in $^{87}$Rb and create a maximally coherent state; this coherence causes the beams to self-focus or self-defocus. A Raman soliton forms when the free-space diffraction is exactly cancelled by the self-focusing effect. We present our recent experimental observations of self-focusing and self-defocusing in this system, the first steps toward atomic Raman solitons. [Preview Abstract] |
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R1.00084: Stationary light and Klein tunneling Johannes Otterbach, Razmik Unanyan, Michael Fleischhauer We discuss the generation and coherent manipulation of stationary pulses of light in atomic ensembles with electromagnetically induced transparency. In particular we discuss the limits on the spatial confinement of these pulses when the latter becomes comparable to the absorption length of the medium. In this case the stationary light field in the dilute gas can be described by a two-component spinor which obeys the two-dimensional Dirac-Weyl equation in an external potential generated by a spatially varying index of refraction. Using analytical and numerical methods, we show that a fundamental lower limit to the spatial confinement arises from Klein tunneling. We determine the linewidth of the resonances in the effective potential and discuss conditions for optimizing spatial confinement and tunneling losses. [Preview Abstract] |
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R1.00085: Quantum Properties of Coated Cell Beamsplitters Michael Hohensee, Mason Klein, Yanhong Xiao, David F. Phillips, Ronald L. Walsworth The demonstration of phase coherent transport of slow light between two separated modes in a paraffin-coated vapor cell suggests that quantum states may be exchanged between two modes via a randomly time-dependent coupling to an intermediate spin ensemble. We show that the efficiency of inter-mode exchange can be enhanced by application of a phase shift to the spin ensemble. Provided that the mode-ensemble coupling is sufficiently slow, the inter-mode coupling can be quite strong, while inhomogeneous losses are a function of the distribution of the ensembles' interaction times. These results suggest that even very classically disordered systems can serve to coherently manipulate quantum states. [Preview Abstract] |
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R1.00086: Optimized slow light and beam profiles Rita Kalra, Mason Klein, Yanhong Xiao, Michael Hohensee, David F. Phillips, Ronald L. Walsworth We will present an overview of Electromagnetically Induced Transparency (EIT) and slow light dependence on transverse laser field profile. Idealized treatments typically assume a uniform optical field profile while experiments are typically performed with gaussian beam profiles. Here we present a comparison of EIT lineshapes measured with flat top and gaussian transverse profiles and compare slow light delays observed under such circumstances with those derived from measured EIT line shapes in simple models. Additionally we study the effects of differential AC Stark shifts due to transverse beam profiles and their effect on light storage. [Preview Abstract] |
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R1.00087: Radiation trapping and other propagation effects in stored light Cleo Leung, Mark Browning, Rita Kalra, Mason Klein, Yanhong Xiao, Michael Hohensee, David F. Phillips, Ronald L. Walsworth In dense atomic media, absorption of signal light propagating under Electromagnetically Induced Transparency (EIT) is typically driven by incomplete polarization of the atomic medium due to mechanisms such as radiation trapping as well as competing nonlinear processes. Additional atomic decoherence arises from mechanisms such as collisions with buffer gas atoms and cell walls, diffusion out of the laser beam, and residual magnetic field gradients. We present a study of such decoherence mechanisms in warm rubidium vapor cells, focusing on the elimination of radiation trapping. We directly measure fluorescence rise times as a diagnostic of radiation trapping in the medium. Additionally, we present improved cell geometries and buffer gases for the reduction of such effects. [Preview Abstract] |
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R1.00088: LASER COOLING AND TRAPPING |
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R1.00089: Entropy Exchange in Laser Cooling H. Metcalf Laser cooling is usually viewed as velocity space compression by a velocity-dependent optical force. Since such forces do not conserve energy, their full description must include the energy added to the light field at a frequency above that of the laser beams by spontaneous emission (SpE). Thus the light field must be part of the system under consideration. It is usually presumed that SpE is necessary to remove the entropy lost by the atoms. A closer look suggests that SpE does this by redistributing the light among the multitude of empty states of the radiation field. Here we show that the laser beams themselves constitute a sufficiently large reservoir of states so that stimulated emission can do precisely the same thing. We compare the entropy lost by the atoms with the entropy capacity of the laser beams. The entropy exchange between the atoms and the laser fields does NOT constitute a loss of entropy but merely its redistribution among parts of the system. Thus it doesn't violate the Liouville theorem or unitarity because neither the total entropy nor the system's phase space volume is reduced, but merely exchanged between its parts. The entropy in the light field is not dissipated until the outgoing beams hit the walls in a non-conservative, irreversible process. The walls are not part of the system, just as the empty modes into which SpE dumps the light are not usually part of it. [Preview Abstract] |
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R1.00090: Towards Trapping and Coupling to Atoms with a Magnetic Cantilever Matthew Eardley, Ying-Ju Wang, Andrew Geraci, John Moreland, Leo Hollberg, John Kitching Our previous results [see Y. Wang et. al, Phys. Rev. Lett. 97, 227602 (2006)] show that a microfabricated mechanical resonator (cantilever) supporting a small magnetic particle can resonantly couple to atomic spins in a mm-scale vapor cell. We now consider such an interaction in a sample of laser-cooled atoms. The same magnetized cantilever should be able to create a trap for these atoms. A magnetic quadrupole trap is created by adding a bias field to the dipole-like field of the magnetic cantilever tip. We propose to study the coupling of the motional excitation of the cantilever to the trapped atoms by inducing Zeeman transitions, which would cause an observable loss of atoms from the trap. The resonant vibration of the magnetic cantilever tip creates the necessary oscillatory field at the Zeeman frequency. We also report on progress in custom fabricating cantilevers with the appropriate parameters, and on transferring cold atoms from a magneto-optical trap to the cantilever trap. Implementing this setup could make possible a variety of experiments in which microfabricated resonators interact resonantly with cold atom spins. [Preview Abstract] |
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R1.00091: Progress towards a Continuous-Wave BEC C. Hempel, R. Mhaskar, M. Traxler, V. Vaidya, S. Olson, G. Raithel We report on progress towards a continuous-wave BEC. A currently operational high-gradient magnetic-guide structure provides us with a beam of cold $^{87}$Rb atoms. The atomic flux in the guide is $\sim 2 \times 10^7$~atoms~s$^{-1}$ with a transverse temperature of 420~$\mu$K and a longitudinal temperature of 1~mK. Simulations suggest that an increased input flux in the guide of $10^9$~atoms~s$^{-1}$ at a temperature of 100~$\mu$K combined with continuous evaporative cooling will enable the system to reach quantum degeneracy. We give an overview of the strategies and recent progress towards achieving this goal, including a Zeeman slower atomic beam source, complete optical isolation of the atomic guide from the injection stage using mechanical shutters and surface adsorption evaporative cooling. An outlook on usage of the atom laser in inertial sensor applications involving spiral guide structure will be discussed. [Preview Abstract] |
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R1.00092: A High-Power, All-Solid-State Laser Source for Laser Cooling of Lithium R.W. Stites, J.R. Williams, E.L. Hazlett, J.H. Huckans, K.M. O'Hara We have constructed a diode-pumped Nd:YVO$_4$ ring laser operating at 1342 nm with an output power of several Watts. This solid state laser is injection locked by a low-power (60 milliWatt) 1342 nm diode laser to force uni-directional, single-frequency operation. The 1342 nm output radiation is frequency doubled in an external build-up cavity which contains a periodically-poled lithium niobate (PPLN) crystal. This system is capable of providing $\approx 1$ Watt of single-frequency light at 671 nm (suitable for exciting the D1 and D2 transitions in $^6$Li or $^7$Li). This system can be scaled to multi-Watt output powers levels at 671 nm by employing a master-oscillator power-amplifier (MOPA) configuration in which the 1342 nm laser light is amplified by a second Nd:YVO$_4$ gain medium prior to frequency doubling. This powerful, narrow linewidth source can be used for laser cooling and trapping of lithium atoms or for providing optical dipole traps and optical lattices near 671 nm. [Preview Abstract] |
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R1.00093: Dynamically adjustable box-like potentials for ultracold atoms E.L. Hazlett, J.H. Huckans, J.R. Williams, R.W. Stites, K.M. O'Hara We describe a technique to construct a box-like potential for ultracold atoms with a dynamically adjustable trapping volume. Our particular interest in such a trap is to provide a nearly homogeneous external confining potential for studies of degenerate fermionic atoms in an optical lattice. We have shown theoretically that by using box-like (rather than harmonic) external confinement, we can prepare fermionic atoms in an optical lattice at extremely low temperatures (relative to the Fermi temperature). The trap will be formed at the intersection of two hollow, blue-detuned laser beams. The hollow laser beams are each produced by passing a focused, high-order Laguerre-gaussian laser beam through an axicon. By adjusting the optical path length between the focusing lens and the axicon, the radius of the hollow region at the location of the trap can be adjusted. We will compare two techniques for generating the high-order Laguerre-gaussian laser beams: a spiral phase plate and a computer generated hologram. [Preview Abstract] |
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R1.00094: Far-off-resonant ring trap near the ends of optical fibers Frank Moscatelli, Charles Sackett, Shengwang Du, Eun Oh We propose that micrometer-sized atom traps can be created using the optical dipole force between the ends of two single-mode optical fibers carrying counterpropagating light beams of two different wavelengths from both fibers. The traps have a simple design that is feasible to implement with commercially available products. They can be used as a flexible ``atom tweezers'' to manipulate atoms in free space without the need for traditional focused laser beams. A particularly interesting feature is the formation of a static ring-shaped trap for properly chosen beam parameters. Furthermore, the ring can be split into two longitudinally adjacent rings. Microscopic ring traps such as this could have important applications in atom interferometry and fundamental investigations of Bose-Einstein condensates. [Preview Abstract] |
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R1.00095: Laser spectroscopy of trapped Th$^{3+}$ ions Adam Steele, Corey Campbell, Layne Churchill, Michael DePalatis, David Naylor, Alex Kuzmich, Michael Chapman We are applying the techniques of laser cooling and ion trapping to investigate the low lying nuclear isomeric state in $^{229}$Th. We will confine Th$^{3+}$ atoms in an RF trap [1] and sympathetically cool them with barium ions. The ions are produced by laser ablation from a thorium metal target by the third harmonic of a Q-switched YAG laser. Using mass-spectroscopic techniques we separate out the Th$^{3+}$ ions from the plume of ablation products. We once trapped we will observe fluorescence from the trapped ions using transitions at 984 nm and 690 nm. [1] Peik E. and Tamm Chr., \textit{Europhysics Letters}, \textbf{61} (2) (2003) [Preview Abstract] |
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R1.00096: The STIRAP-based unitary decelerating and accelerating processes of a single free atom Xijia Miao The STIRAP-based unitary decelerating and accelerating processes have been constructed for the physical system of a single free atom. The present theoretical work is focused on investigating analytically how the momentum distribution of a momentum superposition state of a quantum system such as a momentum Gaussian wave-packet state of a single freely moving atom affects the STIRAP state transfer in these decelerating and accelerating processes. The complete STIRAP state transfer and the unitarity of these processes are stressed highly in the investigation. It has been shown that the momentum distribution has an important influence upon the STIRAP state-transfer efficiency. In the ideal adiabatic condition these unitary decelerating and accelerating processes are studied in detail for a freely moving atom. A general adiabatic condition for the basic STIRAP unitary decelerating and accelerating processes is also derived analytically. The unitary decelerating and accelerating processes may be used to manipulate and control in time and space a Gaussian wave-packet motional state of a free atom. The detail work see: Xijia Miao, http://arxiv.org/abs/quant-ph/0707.0063. [Preview Abstract] |
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R1.00097: Neutral Atom Lithography Using a Bright Metastable Helium Beam Claire Shean, Jason Reeves, Harold Metcalf We have performed neutral atom lithography using a bright beam of metastable Helium (He*) that is collimated with the bichromatic force followed by two Doppler molasses velocity compression stages. We have previously demonstrated this lithography method using a metal grid to project its image on a self assembled monolayer (SAM) of nonanethiol. The open areas of the grid allow incident He* to damage the SAM molecules by depositing their 20 eV of internal energy on the surface. The undisturbed SAM regions then protect a gold coated Silicon wafer from a wet chemical etch. Samples created with this method have an edge resolution of 63 nm that was observed using an atomic force microscope. We have now achieved focusing of the He* beam into lines by the dipole force that the atoms experience while traversing a standing wave of $\lambda$ = 1083 nm light tuned 500 MHz above the $2^3S_1 \longrightarrow 2^3P_2$ transition. The lines are separated by $\lambda$/2 and their length is comparable to the laser beam waist. Because bichromatic collimation makes such an intense He* beam, our exposure time can be as short as 10 minutes. [Preview Abstract] |
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R1.00098: ULTRACOLD COLLISIONS AND PHOTOASSOCIATION PROCESSES |
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R1.00099: Interaction and pairing of atoms in nonzero partial waves at ultracold temperatures Bo Gao We present analytic descriptions of atomic interaction at ultracold temperatures with emphasis on the Feshbach resonances in nonzero partial waves. The results, including formula for binding energies below the threshold and the descriptions of Feshach/shape resonances above the threshold, are derived from the quantum-defect theory. We also introduce a generalized scattering length that is well defined and useful for all partial waves, to replace the traditional definition that fails for $l\ge 2$ due to the long-range van der Waals interaction. [Preview Abstract] |
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R1.00100: Characterization of three-body processes near a magnetic field induced Feshbach resonance Jose P. D'Incao, Brett D. Esry, Chris H. Greene We explore universal and nonuniversal aspects of three-body processes using interatomic interactions that explicitly produce a magnetic field dependent Feshbach resonance. In particular, we studied cases in which the Feshbach resonance has a large background scattering length, characterized by a weakly bound or quasi-bound state in the open channel, and cases where the resonance is unnaturally narrow due to weak coupling between open and closed collision channels. Both types of resonances are currently encountered in experiments with ultracold gases and their influence on the Efimov physics governing three-body processes is largely unexplored. Our results are based on a powerful new technique in which the full hyperfine interaction is included and the three-body scattering processes are described in an intuitive picture in terms of hyperspherical effective potentials. This work was supported by the National Science Foundation and by AFOSR. [Preview Abstract] |
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R1.00101: Generating Efimov molecules by four-body recombination Yujun Wang, B.D. Esry We investigate the formation of Efimov trimer states via four-body collisions involving three resonantly interacting, identical bosons and a fourth distinguishable atom. We assume the interaction with this distinguishable atom is perturbative, allowing us to apply an analytical approach. The recombination probability is characterized by sharp peaks corresponding to Efimov trimer formation. We also present results for the non-resonant boson-boson interaction case. Specifically, we give the scaling behavior when the boson-boson scattering length is large and negative. Finally, we discuss the conditions under which this process might be observed experimentally. [Preview Abstract] |
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R1.00102: Ultracold collisions between atoms and molecules in high vibrational states: effect of the atom-atom scattering length Goulven Qu{\'e}m{\'e}ner, 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. Using a quantum-mechanical formalism based on hyperspherical coordinates, we have obtained elastic and inelastic rate coefficients for the fermionic system $^6$Li + $^6$Li$_2$ and for the bosonic system $^7$Li + $^7$Li$_2$ for molecule in high vibrational states [1]. We explain the Pauli blocking mechanism that occurs in the experiments, by comparing rate coefficients for a system composed of bosonic or fermionic atoms as a function of the atom-atom scattering length. [1] G. Qu{\'e}m{\'e}ner, J.-M. Launay, and P. Honvault, Phys. Rev. A {\bf 75}, 050701(R) (2007). [Preview Abstract] |
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R1.00103: Collisional decoherence of molecular wavepackets at ultracold temperatures Christopher Hemming, Roman Krems We present an analysis of collisional decoherence of molecular superposition states in an ultracold gas. The approach is based on the derivation of a linear differential equation for the time evolution of the reduced density matrix for molecular rotational states. The tetradic decoherence operator is expressed in terms of collision $T$ matrix elements and the decoherence rate is obtained from eigenvalues of this operator. We consider collisional decoherence of rotational wavepackets in a bath of ultracold atoms and decoherence due to identical molecule -- molecule scattering. [Preview Abstract] |
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R1.00104: Differential scattering of cold molecules in external electric and magnetic fields Timur Tscherbul, Roman Krems Previous work has shown that integral cross sections for molecular collisions at low temperatures can be controlled by external electromagnetic fields [1]. Here, we demonstrate that the differential scattering cross sections (DCS) may also be sensitive to external fields. The DCS is a coherent superposition of different partial wave ($\ell$) contributions. Electric fields mix different rotational states, which leads to an indirect coupling of states with different $\ell$, and modifies the angular dependence of the DCS. We show that the DCS for spin depolarization in CaH($^2\Sigma$)--He collisions can be shifted from sideways-peaked (in the absence of an electric field) to forward-peaked (at electric fields of $\sim100$ kV/cm). This can be used to obtain valuable information about the anisotropy of intermolecular interactions [2], design experiments for kinematic slowing of molecules via inelastic collisions [1], and explore the stereodynamics of molecular collisions and chemical reactions~[3]. References: [1]~R.~V.~Krems, Int. Rev. Phys. Chem. {\bf 24}, 99 (2005); [2] U. Buck, Rev. Mod. Phys. {\bf 46}, 369 (1974); [3] D.~Herschbach, Eur. Phys. J. D {\bf 38}, 3 (2006). [Preview Abstract] |
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R1.00105: Ultracold Inelastic Collisions in Two Dimensions Zhiying Li, Sergey Alyabyshev, Roman Krems We analyze collisions of ultracold atoms or molecules confined by a harmonic potential and show that the cross sections for inelastic s-wave scattering have the same energy dependence as in pure 2D geometry. This indicates that chemical reactions and inelastic collisions may be suppressed in an ultracold gas under strong confinement in one dimension. The confinement does not change the energy dependence of inelastic collisions for non-zero partial waves. We present a numerical proof of the threshold collision laws in 2D. Our derivation and calculations demonstrate that ultracold collisions accompanied with changes of angular momentum in 2D must be suppressed, which indicates that inelastic collisions of atoms or molecules in the presence of weak electromagnetic fields may be controlled by varying the orientation of the external field axis with respect to the plane of confinement. [Preview Abstract] |
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R1.00106: Studies of Ultracold Strontium Atoms in an Optical Dipole Trap A.J. Traverso, Y.N. Martinez de Escobar, P.G. Mickelson, 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 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 (ODT). We examine the loading characteristics, thermalization, and lifetime of atoms held within the ODT. We also perform spectroscopy of atoms held within the ODT. During laser cooling, we are able to manipulate the energy levels of the atoms and shelve them into metastable states using 707 nm and 3 $\mu$m lasers. These experiments reveal interesting physics of ultracold strontium. [Preview Abstract] |
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R1.00107: Progress towards forming ultracold $^{85}$Rb$_2$ molecules in an optical trap H.K. Pechkis, M. Bellos, J. RayMajumder, R. Carollo, E.E. Eyler, P.L. Gould, W.C. Stwalley We are completing construction of an apparatus for efficiently producing ultracold Rb$_2$ molecules in a quasi electro-static optical trap (QUEST) by photoassociation (PA). The QUEST is loaded from a magneto-optical trap (MOT), with additional cooling and compression stages to optimize the density and temperature. The trapped atom cloud is detected by absorption imaging. Molecules will be formed from the optically trapped atoms by PA to levels bound by $\simeq$ 1-100 cm$^{-1}$, followed by radiative decay. Employing the QUEST will allow optical trapping of Rb$_2$ in the singlet $X\,^1\Sigma_g^+$ state, as well as enhancing greatly the PA rates for forming these ultracold molecules. We will present in more detail our progress in experimentally forming ultracold molecules in the dipole trap and progress toward experiments on collisions involving the trapped molecules. This work is supported by National Science Foundation. [Preview Abstract] |
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R1.00108: Semi-classical study of cold inelastic dipole-dipole collisions Catherine Newell, Michael Cavagnero, Vladimir Roudnev Inelastic collision cross-sections for polar molecules in static electric fields are calculated semi-classically. The molecules are modeled as polar rigid-rotors in low-field seeking states. Our analysis treats two-body collisions between such low-field seeking dipoles at various temperatures in the cold and ultracold regimes, and is applicable to several molecular species. We examine in detail partial cross-sections for the production of high-field seeking states, and the dependence of these cross-sections on the angle of incidence with respect to the external field direction. The degree to which rotationally inelastic collisions are impulsive, as opposed to perturbative, is assessed. [Preview Abstract] |
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R1.00109: Anisotropic threshold scattering in ultracold dipolar gases Vladimir Roudnev, Michael Cavagnero The Born-Oppenheimer representation is used to calculate dipole-dipole scattering at cold and ultracold temperatures in an external electric field. Sufficiently close to threshold, scattering is dominated by only a few adiabatic channels, providing a simple picture of the scattering dynamics. The low-energy scattering cross section is driven by two types of resonances: near-threshold bound states in the lowest adiabatic channel and Feshbach/shape resonances due to the coupling between the lowest and first excited channels. The resonances of the second kind produce extremely sharp peaks in the elastic scattering cross section. In the vicinity of the peaks scattering is predominantely isotropic and can be parametrized by an effective s-wave scattering length. When the cross section is small, however, the anisotropy of the dipole-dipole interaction results in a strongly energy-dependent spacial anisotropy in near-threshold collisions. [Preview Abstract] |
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R1.00110: Novel photoassociation scheme toward the production of ultracold ground state Cesium molecules Matthieu Viteau, Amodsen Chotia, Maria Allegrini, Daniel Comparat, Pierre Pillet It is proposed that bound states of ultracold Cs2 molecules in their ground singlet state can be produced by a novel photoassociation scheme. In particular, the final goal is to efficiently convert the population into true ground state (v=0, J=0) ultracold molecules. Indeed, a dense sample of ultracold molecules with neither vibration nor rotation would open the way to further important experiments from controlled chemistry to a Bose-Einstein molecular condensate. Photoassociation of cold atoms in a high vibrational level ($^{1}\Sigma _{g}^{+}$ or $^{3}\Sigma _{u}^{+})$ is followed by an optical pumping scheme by a shaped femtosecond laser. The broadband character of the femtosecond laser is used to excite the molecules to potentials that efficiently decay to lower vibrational levels and to modify the vibrational distribution. The first experimental attempts have revealed a reduction of the number of detected cold molecules. Simple rate-equation models of the dynamics have shown that optical pumping can be the predominant process. [Preview Abstract] |
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R1.00111: Manipulating Phase to Enhance Ultrafast Photoassociative Ionization G. Veshapidze, M.L. Trachy, H. Jang, C.W. Fehrenbach, B.D. DePaola With their broad bandwidths and high degree of coherence, ultrafast lasers hold the promise of efficiently guiding chemical reactions along desired pathways. In this work, we experimentally examine the effects of spectral phase on a prototypical system and process, namely ultra cold atomic rubidium undergoing photoassociation followed by coherent excitation and ionization (PAI). We concentrate on simple, readily modeled spectral phase functions such as \begin{eqnarray*} \phi(\omega)&=& A \sin \left[ \left( \omega-\omega_0 \right)T + \phi_0 \right]\\ \phi(\omega)&=&\left\{ \begin{array}{rl} 0 &\mbox{ if $\omega < \omega_0$} \\ \pi &\mbox{ if $\omega \ge \omega_0$} \end{array} \right.\\ \phi(\omega)&=&\left\{ \begin{array}{rl} \pm \frac{\pi}{2} &\mbox{ if $\omega_L \le \omega \le \omega_U$} \\ 0 &\mbox{ otherwise} \end{array} \right. \end{eqnarray*} That is, we concentrate on sinusoidal phase, $\pi$-phase steps, and $\frac{\pi}{2}$-phase pulses. When combined with high resolution time-of-flight spectroscopy as a diagnostic, we find that such phase control can yield a tremendous amount of information about the PAI process. The experimental measurements will be compared with the results of simple calculations. [Preview Abstract] |
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R1.00112: Molecular formation and alignment of photo-associated cold atoms using ultrafast laser pulses. Kyle Taylor, Michell Stephens, Karen Chamberlin, Steve Lynam, Christopher Verzani, Hai Nguyen We present a new experimental research program that focuses on photo-association of cold trapped atoms by ultrafast laser interaction. Molecular formation at $\mu $K temperatures offers opportunities to study new phenomena in chemistry, metrology, and even quantum physics. In this work, an ultrafast laser system in conjunction with magneto optical trap recoil ion momentum spectroscopy (MOTRIMS) will be employed to investigate the products formed in the interaction of ultrafast laser pulses with cold trapped $^{87}$Rb atoms. We investigate various processes of molecular photo-association which include formation, distribution of populations, and alignment. The diagnostic system and the specific photo-association process will be described in detail. [Preview Abstract] |
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R1.00113: Analytical Calculation of the Scattering Length in Antihydrogen-Atom Collisions Gleb Gribakin, Svante Jonsell, Alastair Thompson We have extended the method of [1] to cold antihydrogen-atom collisions. The scattering length is determined by the mean scattering length $\bar a = 0.478 (2mC_6)^{1/4}$, where $m$ is the reduced mass and $C_6$ the van der Waals constant (in atomic units), and the semiclassical phase at zero energy. In addition, the antiproton-nucleus interaction is included through the strong-force scattering length $a_{\rm sf}$, whose imaginary part accounts for the antiproton annihilation. Our final result is \begin{displaymath} a=\bar{a}\left[1-\frac{1-a_0/\bar a-2\pi a_{\rm sf}/a_c} {1+(1-a_0/\bar a)(2\pi a_{\rm sf}/a_c)}\right], \end{displaymath} where $a_0$ is the scattering length found neglecting the strong interaction, and $a_c=(mZ)^{-1}$ is the antiproton-atom Coulomb radius. Our value for for hydrogen agrees with [2]. Estimates are made for the noble gas atoms. \begin{enumerate}\setlength{\itemsep}{-3pt}\setlength{\itemindent}{-12pt} \item G. F. Gribakin and V. V. Flambaum, Phys. Rev. A {\bf 48}, 546 (1993). \item S. Jonsell et al., J. Phys. B {\bf 37}, 1195 (2004); E. A. G. Armour, Y. Liu and A. Vigier, {\em ibid.} {\bf 38}, L47 (2005). \end{enumerate} [Preview Abstract] |
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R1.00114: Formation of ultracold molecules in chemical reactions Timur Tscherbul, Girts Barinovs, Jacek Klos, Roman Krems We demonstrate that chemical reactions in collisions of high-energy molecular beams can generally produce molecules with zero velocity in the laboratory-fixed frame. Our analysis shows that collisions of beams may simultaneously yield slow reactant molecules and slow products. The reaction products are formed in selected ro-vibrational states and scattered in a specific direction, which can be controlled by tuning the kinetic energies of the incident beams and the angle between the beams. We suggest that chemical reactions involving alkali metal dimers may be particularly suitable for producing slow molecules in crossed beams. Our calculations show that chemical reactions of polar alkali metal dimers are barrierless. [Preview Abstract] |
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R1.00115: Quantum dynamics of ultracold atom-molecule and molecule-molecule systems Goulven Qu{\'e}m{\'e}ner, Balakrishnan Naduvalath, Roman Krems We report here on our recent progress on reactive atom-molecule and inelastic 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 and vibrational excitation of the molecule on the reactivity. Taking the F+HCl reaction as an illustrative example we also explore the validity of the coupled-states approximation for chemical reactions at cold and ultracold temperatures. 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 [1]. We show that energy transfer in molecule-molecule collisions can be highly efficient and selective when the internal energy and total rotational angular momentum of the colliding molecules are simultaneously conserved. [1] G. Qu{\'e}m{\'e}ner, N. Balakrishnan, and R. V. Krems, arXiv:0709.3081v2 [quant-ph] (2007). [Preview Abstract] |
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R1.00116: Genuine two-channel calculations of 3-body bound states and resonances Juan Blandon, Viatcheslav Kokoouline We present a method to carry out genuine two-channel calculations of 3-body bound and quasi-bound states. Our model potential consist of two 3-body potential surfaces interacting through a localized coupling. The method allows us to obtain 3-body bound state energies and resonance lifetimes. The method employs the 'slow' variable discretization method [1], and complex absorbing potential for lifetime calculations. It can be used with long-range and short-range potentials. Particularly, it can be used to calculate true 3-body Feshbach resonances, including Efimov-type states. \newline \newline [1] O.~I.~Tolstikhin, S.~Watanabe, and M.~Matsuzawa, J. Phys. B: At. Mol. Opt. Phys. {\bf 29}, L389 (1996). [Preview Abstract] |
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R1.00117: Correlated Gaussian Hyperspherical Method for Few-Body Systems Javier von Stecher, Chris H. Greene We develop an innovating numerical technique to solve few-body systems. In this numerical method, correlated Gaussian basis functions are used to expand the channel functions in the hyperspherical representation. The simple form of the basis functions reduces the computational demands of the matrix elements calculations which allow us to efficiently solve four-body systems. The optimization techniques of the correlated Gaussian method are applied to these hyperspherical calculations in order to control the convergence. The method is applied to few-body systems with short-range interactions and several properties of the three- and four-body systems are obtained. [Preview Abstract] |
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R1.00118: Revisited LeRoy-Bernstein formula for weakly bound molecules Laurence Pruvost, Haikel Jelassi, Bruno Viaris de Lesegno The energy law giving the eigen energies of a -cn/Rn-cm/Rm potential (studied by LeRoy in 1980 [1]) is revisited. For n=3, m=6, an analytical law giving the density of states is deduced. In the context of weakly bound levels an energy law giving the vibrational number v versus the binding energy is given. We show that the well-known LeRoy-Bernstein formula [2] [3] has to be corrected by additional terms, with the first one varying as the binding energy , the second one as its square and the third as a power to 7/6. The use of such a law is discussed in the context of the photo-association spectroscopy of long range molecular levels. References [1] Theory of deviations from the limiting near-dissociation behaviour of diatomic molecules, R. J. LeRoy, J. Chem. Phys. 73, 6003 (1980). [2] Dissociation energy and long-range potential of diatomic molecules from vibrational spacings of higher levels, R. J. LeRoy and R. B. Bernstein, J. Chem. Phys. 52, 3869 (1970). [3] The Dissociation Energy of the Hydrogen Molecule Using Long-Range Forces, W. C. Stwalley, Chem. Phys. Lett. 6, 241,1970. [Preview Abstract] |
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R1.00119: A wide-open molecular magnetic trap for collision studies Benjamin Stuhl, Brian Sawyer, Mark Yeo, Dajun Wang, Benjamin Lev, Jun Ye Cold molecular collision studies hold the potential of revolutionizing our understanding of chemical and molecular dynamics, both on Earth and astrophysically. Toward this end, we have developed and implemented a magneto-electrostatic trap with near-360\r{ }circumferential access for optical or molecular beam probes. The trap has demonstrated almost optimal loading efficiency, yielding a trapped density of 10$^{6}$ cm$^{-3}$ at a temperature of 70 mK. We also report further progress towards the goal of cold molecular collisions. [Preview Abstract] |
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R1.00120: Sensitive detection of polar molecules Noah Fitch, Paul Parazzoli, Heather Lewandowski Efficient state-sensitive detection of molecules is required to explore cold molecular interactions. We utilize laser induced fluorescence and resonance enhanced multi photon ionization (REMPI) detection schemes to determine both the internal and external properties of our molecular samples before and after the collisions. The information about initial and final states allows for a more complete interpretation of the collision dynamics. [Preview Abstract] |
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R1.00121: APPLICATIONS OF AMO SCIENCE |
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R1.00122: Multiphoton Microscope for Shaped Pulse Microscopy Michael Murphy, Brett J. Pearson, Thomas Weinacht Multiphoton microscopy is a developing field in which ultrashort laser pulses are used to drive multiphoton processes in a (typically) biological specimen. Multiphoton microscopy can have many advantages over traditional confocal microscopy, including a well-defined excitation volume, deeper sample penetration, and reduced specimen damage. Additionally, the broadband laser sources used in multiphoton microscopy allow one to shape the excitation pulse to selectively drive different processes. We are constructing a multiphoton microscope to be used for shaped pulse microscopy in an undergraduate research laboratory. Although the initial design will be for two-photon imaging of fluorescent proteins, the arrangement could be adapted for other forms of multiphoton microscopy as well (e.g. third-harmonic). By incorporating a broadband pulse shaper into the optical design, we will be able to seek closed-loop discrimination between different fluorescent samples. Furthermore, the use of a two-dimensional SLM in a Fourier-based pulse shaper should allow for fast switching between pulse shapes. [Preview Abstract] |
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R1.00123: Back-reaction and dipolar interaction noise of a spin magnetometer Seung-Kyun Lee, M.V. Romalis An atomic magnetometer detects magnetic field through magnetic resonance of atomic spins, and competes in its sensitivity with a superconducting quantum interference device (SQUID). In this work we compare the fundamental quantum noise of a dc SQUID with that of a spin-based magnetometer. In particular, we calculate the back-reaction noise of a generic spin magnetometer coupled to an input coil, and show that a linear amplifier built from such a magnetometer is bound by a universal noise limit derived from the uncertainty principle. Dipolar spin-spin interaction is a fundamental physical process which affects decoherence and fluctuation in a spin magnetometer. We argue that an isolated magnetometer dominated by such interaction can reach a magnetic field sensitivity many orders of magnitude higher than that of a dc SQUID, and present numerical examples based on observed decoherence times in various atomic spin systems. [Preview Abstract] |
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R1.00124: Developments in chip scale atomic magnetometers W. Clark Griffith, Ricardo Jimenez-Martinez, Vishal Shah, Svenja Knappe, John Kitching Microfabrication techniques developed at NIST have led to the demonstration [1] of a chip-scale atomic magnetometer (CSAM) with a sensitivity of 5 pT/Hz$^{1/2}$, using $M_x$ modulation in a 2x1x1 mm $^{87}$Rb vapor cell. An alternative to the $M_x$ technique is Bell-Bloom modulation of the optical pumping light [2]. This is advantageous in a CSAM since it allows for a simpler device, and it eliminates a source of heading error due to possible misalignment of the light beam relative to the $M_x$ rf coils. We have demonstrated that Bell-Bloom modulation gives comparable magnetometer performance compared to $M_x$ in a millimeter scale vapor cell. We have also achieved 70 fT/Hz$^{1/2}$ sensitivity in a microfabricated vapor cell by operating near zero magnetic field in the SERF regime [3]. The addition of high permeability flux concentrators near the vapor cell amplifies the applied field by a factor of 10 to 100 depending on the geometry. This can potentially push the sensitivity close to the femtotesla level, comparable to low-$T_c$ SQUID sensors, but in a non-cryogenic, simple, low-power device. \\[1ex] [1] P.D.D. Schwindt {\it et al.}, App. Phys. Lett., {\bf 90}, 081102 (2007). \newline [2] W.E. Bell and A.L. Bloom, Phys. Rev. Lett., {\bf 6}, 280 (1961). \newline [3] V. Shah, {\it et al.}, Nature Photonics, {\bf 1}, 649 (2007). [Preview Abstract] |
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R1.00125: Calculations of M-squared values for clipped focused Gaussian beams using vector diffraction theory Glen Gillen, Kendra Baughman Vector diffraction theory is applied to apertured Gaussian laser beam propagation. The computational model developed treats the light field as a 6-component vector electromagnetic wave. None of the commonly employed approximations are assumed (i.e., ray optics, scalar field approximations, paraxial approximations, wavelengths much smaller than longitudinal or tangential distances, etc.) A conductive circular aperture is placed in a converging Gaussian laser beam. Light field distributions beyond the aperture and within the focal region are investigated as a function of the clipping ratio (the ratio of the aperture radius to the Gaussian beam width in the diffraction plane.) The effects of a variety of clipping ratios on the field's maximum intensity and the beam's M-squared value are investigated. [Preview Abstract] |
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R1.00126: Tuning the UV-blue absorption and emission of CdSe {\&} ZnS core-shell nanoparticles by laser radiation Ignacio Gallardo, Kay Hoffmann, Keto John CdSe and ZnS core-shell nanoparticles made by LAM (Laser Ablation of Microparticles) show photoluminesence (PL) peaks in a region of wavelengths below 400nm. Control over the size and PL peak position is obtained by irradiating the nanoparticles multiple times. In LAM, micropaticle powder passes through an aerosol generator and then into a laser ablation glass cell, where a laser pulse (high energy excimer laser) ablates the microparticle aerosol. Nanoparticles are formed after condensation. At this stage the nanoparticles can be covered with a second material or irradiated multiple times to change their size. The size distribution of these particles is successfully investigated with TEM (Transmission Electron Microscopy). PL blue shifts are seen as the mean size decreases. A thermodynamic numerical calculation based on evaporation models and Mie absorption during the LAM process supports the blue shifting of the PL peaks by showing a decrease in particle size as they are exposed to multiple laser irradiations. [Preview Abstract] |
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R1.00127: Strong Localization of Positive Charge in DNA Dmitry Uskov, Alex Burin The positive charge transfer in a DNA molecule is determined by two main factors: the structure and composition of specific DNA strand, and interaction of a positive charge with the DNA environment. In this letter we present results of microscopic linear response theory for balance of charge transfer reaction in synthetic strands GAGG and GAGGG, where experimental data on the rates of electron hole migration has been reported by Lewis et al \textit{Nature}, \textbf{406}, 51-53 (2000). Our theoretical predictions, based on experimental data for the ratio of reaction rates $G^+A(G)_n \leftrightarrow GA(G)_n^+ $, $n=2,3$, suggest that charge in DNA is strongly localized within the single base pair because of the self-induced reorganization of classical environment. The onset of localization has a threshold behavior characteristic to quantum bistability. We also demonstrate that our conclusion does not depend on details of the model. [Preview Abstract] |
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R1.00128: Mass-selective resonance enhanced two-photon ionization laser spectroscopy of hydrated biomolecules Pengqian Wang The various functions of biomolecules are essentially determined by their geometric and energetic structures. Because of the ubiquitous presence of water in living organisms, biomolecules are often hydrated with water molecules, which crucially influence the functionality of the biomolecules. We study the structure and dynamics of mono- and poly-hydrated biomolecules by mass-selective resonance enhanced two-photon ionization laser spectroscopy. A tunable ultraviolet laser is used to excite the hydrated clusters, and a second photon is used to ionize the clusters. The resultant ions are measured by a mass spectrometer. The vibrational structures of the hydrated biomolecules are obtained by comparing the experimental spectra with the results of advanced ab initio quantum chemical calculations. We plan to apply this technique to explore the nucleobases, which are the fundamental building blocks of DNA and RNA molecules. This study provides valuable information on the binding properties of the water molecules around the central biomolecules, as well as on the changes of the structure and tautomeric equilibrium of biomolecules in an aqueous environment. Project supported by the WIU-URC grant. [Preview Abstract] |
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R1.00129: Collisional-radiative model for Tungsten Plasma and Applications for ITER Foster Lewis, James Colgan, Joseph Abdallah Jr. Controlled fusion tokamaks such as ITER present challenging theoretical plasma modeling issues. Since the divertor region of ITER will be coated with tungsten, accurate collisional-radiative (CR) models are required to understand the high radiative power losses associated with tungsten. The energy loss due to radiative processes for high-Z ions can be critical in understanding the ionization balance of the plasma. We present non-local thermodynamic equilibrium (non-LTE) calculations for a tungsten plasma using the Los Alamos National Laboratory suite of atomic codes. We examine the radiated power losses and ion balance distributions for a variety of electron temperatures ranging from 2 keV to 30 keV and densities associated with conditions found in ITER. [Preview Abstract] |
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R1.00130: SPR Effect in Nichrome Alloy Chris Leibs, Ian Ross, Maarij Syed, Azad Siahmakoun We have performed surface plasmon resonance (SPR) experiments in the Kretchmann configuration on prisms coated with 500$\pm $10 nm single metal and alloy thin-films. The thin films are grown by magnetron sputtering and are binary alloy films (Nickel/Chrome with 80/20 concentration). In addition, for comparison we will also present results for pure metal films (Nickel and Chromium). We have observed a pronounce SPR signal at 41.24$^{\circ} \quad \pm $0.01at 633 nm for the Nichrome film while neither of the metal thin-films (Ni or Cr) yields an SPR effect. Aided by the surface morphology and the SPR signal observations, we modeled the effective dielectric constant of the metal alloy by comparing the SPR response of the alloy to that of the individual metal films. We will also show how SPR results can be better understood by analyzing the SPR data correlated with ellipsometric data obtained from these films as well as x-ray analysis (for composition and structure information), and AFM analysis (for surface topography). [Preview Abstract] |
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R1.00131: Chaotic Escape of Particles from a Vase-shaped Cavity: Theory and Experiment Jaison Novick, Kevin Mitchell, Len Keeler, John Delos We study the escape of particles from a two dimensional, specularly-reflecting open vase-shaped cavity. The narrowest point of the vase's neck defines a dividing surface between particles that escape without return and those turned back into the vase. We find trajectories whose path displays a sensitive dependence on launch angle. For our analysis, we consider a point burst of particles emitted in all directions and record the time to reach the vase's neck. We find that this escape time versus the launch angle displays a complex fractal structure. First, we outline a topological theory that predicts a subset of the fractals seen in numerical simulations. We perform a simulation of classical trajectories and compare the simulated fractal to the theoretical prediction. Through a collaborative effort we have experimentally verified the early fractal structure in the escape time using ultrasound. A microphone was placed along the vase's neck to record escaping pulses. We find that classical trajectories arriving at the microphone positions arrive very near the times at which the experimental signal is strongest. [Preview Abstract] |
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R1.00132: Collisional properties quantum halo dimer Steven Knoop, Francesca Ferlaino, Martin Berninger, Michael Mark, Hanns-Christoph Naegerl, Rudolf Grimm We present our latest experimental findings on ultracold (30-250 nK) atom-dimer and dimer-dimer collisions involving Cs Feshbach molecules. In particular we have studied the collisional properties of the universal quantum halo dimer. Resonant enhancement of the atom-dimer relaxation rate is observed in a system of three identical bosons and interpreted as being induced by a trimer state, possibly an Efimov state. A strong magnetic field dependence of the atom-dimer relaxation rate is also observed when the atoms are transferred to a different hyperfine sublevel. For collisions between quantum halo dimers the relaxation rate show a strong scattering length dependence and we find a pronounced minimum of relaxation rate coefficient connected to a substantial suppression of the inelastic loss. Moreover, we observe that inelastic collisional decay can be further suppressed by decreasing the temperature of the ultracold sample. [Preview Abstract] |
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R1.00133: POST-DEADLINE ABSTRACTS |
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R1.00134: Sensitivity of atomic wavefunctions and probability densities to confinement parameters Pranawa C. Deshmukh, Hari R. Varma Studies of confined atoms have attracted considerable attention in recent years [1, 2]. We have studied the sensitivity of atomic wavefunctions and probability densities to confinement parameters using the Dirac-Fock self-consistent field method. The confinement potential is modelled as an annular attractive potential of a certain radius, width and depth which we have varied parametrically to examine dependence of atomic wavefunctions on these parameters. We present in this work studies on the dependence of the wavefunctions of @Ca and the corresponding probability distribution. We find that all but the outermost 4s wavefunctions are relatively insensitive to the cage parameters but the 4s wavefunction is sensitive to both the inner radius and the depth of the potential. References: 1.V. K. Dolmatov, A. S. Baltenkov, J. --P. Connerade and S. T. Manson Rad. Phys. and Chem. 70 417 (2004) 2.M. E. Madjet, Himadri S. Chakaraborty and S. T. Manson Phys. Rev. Lett. 99 243003 (2007) 3.I. P. Grant Springer Series of Atomic, Optical and Plasma Physics (Springer --Verlag, New York 2006) [Preview Abstract] |
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R1.00135: Cold Multiphoton Matrix Assisted Laser Desorption/Ionization (MALDI) Peter Harris, William Cooke, Eugene Tracy We present evidence of a cold multiphoton MALDI process occurring at a Room Temperature Ionic Liquid (RTIL)/metal interface. Our RTIL, 1-Butyl-3-methylimidazolium hexafluorophosphate, remains a stable liquid at room temperatures, even at pressures lower than 10$^{-9}$ torr. We focus the 2$^{nd}$ harmonic of a pulsed (2ns pulse length) Nd:YAG laser onto a gold grid coated with RTIL to generate a cold (narrow velocity spread) ion source with temporal resolution comparable to current MALDI ion sources. Unlike conventional MALDI, we believe multiphoton MALDI does not rely on collisional ionization within the ejection plume, and thus produces large signals at laser intensities just above threshold. Removing the collisional ionization process allow us to eject material from smaller regions of a sample, enhancing the suitability of multiphoton MALDI as an ion imaging technique. [Preview Abstract] |
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R1.00136: Parametric Excitation in a Magneto-optical Trap with Modulating the Magnetic Field Gradient Chang-Woo Lee, Yonghee Kim, Myoung-Sum Heo, Wonho Jhe Parametric resonance is a very interesting and important mechanism in diverse systems from physics to biology. Recently there have been a lot of researches related to the parametric excitation in the magneto-optical trap system. However, the previous investigations were conducted by modulating only the cooling laser intensity. While the study using intensity modulation showed the limit cycle motion and Hopf bifurcation, the magnetic field gradient modulation revealed much more interesting phenomena such as period doubling, chaos, and so on. We have studied the transition problems between two attractors in period doubling area which are much far from equilibrium and could not be understood by the method used in limit cycle motion. The magnetic field modulation methods could give quantitative comprehension of transition problems in the non-equilibrium system that has not been studied. [Preview Abstract] |
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R1.00137: The mass, energy, space and time system theory-MEST Dayong Cao Things have their own system of mass, energy, space and time of themself. (The MEST for short thereinafter). Mass is density, energy is force, time is frequency, spac is amplitude square. In quantum mechanics, the quality of radiate wave mainly is quantum space-time while it's mass-energy is ancillary; The nature of the macrosubstance is mainly mass-energy while space-time are ancillary. Mass-energy are like the earth center while space-time are like the heaven around. An Nuclear of an atom is like the earth center while the charge cloud of an atom(radiate wave) is like the heaven around. Macro is like the earth center while micro is like the heaven around. Physics system of The MEST of heaven and earth, which unites both macrophysics and microphysics. There are the transmutation between space-time and mass-energy. When they get a balance, they get the inertia and eigenvalue system. The inertia, eigenvalue and the transmutative balance system equation are being put forward. New mass-energy wave equation, space-time particle equation and new photoelectric conversion equation are being put forward, With anode dark current of hole, give a new explain to the photoelectric effect experiment;and get new mass-energy equation which equal the mass-energy relation of Einstein. It can be prove by orbit equations of nine planes and orbit equations of electron of H and He. Quantum space-time theory and speed of light theory are being put forward, and explain wave-particle duality and probability of wave, deduce the new uncertainty principle, uncertainty and probability can not be divided. MEST equation of star and black hole are being put forward. [Preview Abstract] |
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R1.00138: Schlieren Imaging with a Dynamic Phase Mask Kelly Kluttz, Jan Chaloupka Optical phenomena that manifest themselves as variations in the phase of the incident light, but not the amplitude, are normally invisible to the eye. A traditional Schlieren imaging system uses a knife edge at its focal plane to generate high-contrast images of these ``phase objects.'' In our numerical simulations, a phase mask replaces the knife edge; we show that the output images are greatly improved, both in intensity and contrast. We also show that different phase masks result in images of varying quality, some of which reproduce the source phase information more faithfully than others. Through the use of a dynamic phase mask, such as with a liquid crystal spatial light modulator (SLM), the output image could be optimized by modifying the phase mask written to the SLM in real time. [Preview Abstract] |
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R1.00139: Experiments in a one-dimensional incommensurate lattice E.E. Edwards, M. Beeler, Jennifer Robinson, Tao Hong, S.L. Rolston We investigate the effects of loading a $^{87}$Rb Bose-Einstein condensate into a one-dimensional optical potential comprised of a shallow primary lattice with an additional weak, perturbing lattice of incommensurate period. The ratio of the primary to secondary lattice period is approximately 0.8. This scheme has previously been shown to mimic a weakly disordered potential. Matter-wave interference patterns from BECs released from the combined lattices show momentum peak separations corresponding to both the spatial periods of the individual lattices as well as the difference frequency. The presence of the beat frequency peaks is dependent on the external trapping potential and lattice strengths. The appearance of these peaks must be due to non-linear interactions, which create coupling between the two lattices. This behavior is surprising considering the shallow depth ($\le $ 0.2 E$_{R})$ of the perturbing lattice. [Preview Abstract] |
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R1.00140: Intrinsic Gas-Phase Spin Relaxation of $^{129}$Xe B.C. Anger, M.S. Solum, R.J. Pugmire, B. Saam Hyperpolarized (HP) $^{129}$Xe produced through spin-exchange optical pumping (SEOP) techniques is useful for many NMR and MRI applications. At gas densities typical for SEOP, fluctuations in the spin-rotation and chemical shift anisotropy interactions mediated by the formation and breakup of loosely bound $^{129}$Xe-Xe molecules have recently been identified as the primary intrinsic spin relaxation mechanism, with $T_1$ limits as short as $\approx 5$~hours for samples of pure Xe. We have shown that this relaxation mechanism can be suppressed at high magnetic fields, leading to $T_1$ relaxation times of $\approx 100$~h at 14.1~T. Further results showed a near doubling of relaxation times with moderate temperature increases from 293~K to 393~K, implying a maximum intrinsic relaxation time of $\approx 9$~h at 393~K. In the field regime practical for SEOP (2.8~mT), we observed $^{129}$Xe relaxation times of nearly 5 hours in a 1~amagat Xe sample at 393~K. These results suggest a practical, low-field, non-cryogenic storage system that will provide Xe hold times much longer than those currently available from standard cryogenic storage systems on flow-through Xe polarizers. [Preview Abstract] |
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R1.00141: Ion Trap for efficient single Photon-Atom Coupling Robert Maiwald, Markus Sondermann, Gerd Leuchs, James C. Bergquist, Dietrich Leibfried, Joe Britton, David J. Wineland Excitation of a single atom by a single photon is a fundamental process of physics, yet fairly inefficient in today's realizations. We present the design of a compact ion trap with superior optical access compared to conventional designs that allows for the localization of an ion in the focal point of a deep parabolic mirror. The electrode geometry results in a trapping potential that follows the axial symmetry of the mirror and provides optical access to the ion from almost the entire solid angle. The latter property is essential for efficient coupling of single ions to single photons in free space. The trap design can be adapted for other applications by replacing the mirror by a planar electrode. Using this more general design the ion can still be optically accessed from at least half to over 90{\%} of the solid angle. The generation of a suitable mode-matched, dipole-like excitation pattern is discussed as well. Applications of an efficient light-matter coupling scheme include decoherence studies, quantum repeaters and quantum memories. [Preview Abstract] |
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R1.00142: Test of Particle-Assisted Tunneling for Strongly Interacting Fermions in an Optical Superlattice Tim Goodman, Luming Duan Fermions in an optical lattice near a wide Feshbach resonance are expected to be described by an effective Hamiltonian which is equivalent to the general Hubbard model (GHM), with particle-assisted tunneling rates resulting from the strong atomic interaction. [Phys. Rev. Lett. 95, 243202 (2005).] Here, we propose a scheme to unambiguously test the predictions of this effective Hamiltonian through manipulation of ultracold atoms in an inhomogeneous optical superlattice. The superlattice potential separates the lattice into an array of independent double wells, allowing an exact solution of the GHM which can be compared with experimental observations. In practical experimental configurations the presence of a global harmonic trap makes each double well slightly different, and the measured time-of-flight images involve signals that are averaged over all potential wells. In spite of this complication, we show that under appropriate manipulation of the lattice barrier and the! external magnetic field, one can reconstruct precisely the two-site dynamics from the time-of-flight images. This provides a quantitative testbed to compare theory with experiments in the strongly interacting region. The proposed measurement also allows us to infer the structure of the low energy Hilbert space, directly testing a key assumption in the derivation of the effective Hamiltonian, and it allows a complete empirical determination of all the parameters in the effective GHM, including the particle-assisted tunneling rates. [Preview Abstract] |
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R1.00143: Constraints on the Time-Dependence of the Speed of Light from Lunar Laser Ranging Felix T. Smith With the help of lunar laser ranging (LLR) data it is proposed to establish experimental constraints on the time dependence of the velocity of light (or, with the present defined value for $c$, in the effective length scale). Since 1994 the LLR measures of lunar distance have been accurate to a few parts in 10$^{10}$ [J.B.R. Battat et al., PRL, \textbf{99}, 241103 (2007)]. By a revised data analysis these may suffice to reveal changes in $c$ over a decade if its time constant is comparable to the Hubble expansion. Accuracy could be improved by emphasizing the tectonically stable moon as a scale of length for measurements. The lunar retroreflector L2, one of four now operative, is more distant from Earth than the others by distances as great as 300 km. Sensitivity to \textit{dc/dt} could be improved by closely spaced measurements of the difference between the signal times to L2 and the other reflectors, reducing the effect of terrestrial movements on the analysis. The current Apache Point project is expected to improve sensitivity by a factor of 10 or 20 [J.G. Williams et al. (gr-qc/0311021) (2003)]. Sensitivity might also be improved eventually by interferometric methods. [Preview Abstract] |
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R1.00144: Observation of a 2D Bose-gas: from thermal to quasi-condensate to superfluid Anand Ramanthan, Pierre Clad\'e, Changhyun Ryu, Kristian Helmerson, William Phillips We present experimental results on a Bose gas in the quasi-2D geometry near the Berezinskii, Kosterlitz and Thouless (BKT) transition temperature. By measuring the density profile, in situ and after time of flight, and the coherence length of the gas, we identify different states of the gas. In particular, we observe that the gas develops a bimodal distribution without long range order. In this state, the gas presents a longer coherence length than the thermal cloud; it is quasi-condensed, but not superfluid. Experimental evidence seems to indicate that we are observing the transition towards superfluidity (BKT transition). [Preview Abstract] |
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R1.00145: Progress toward probing the electron electric dipole moment using the PbF molecule: The lifetime of the D state of PbF Poopalasingam Sivakumar, Christopher McRaven, Neil Shafer-Ray The lead fluoride molecule has many features that may prove advantageous to a measurement of the electron's electric dipole moment (the e-edm.) Among these features is a X-A-D doubly resonant enhanced multi photon ionization process that allows for pseudo-continuous state selective detection. Critical to the design of a laser system to take full advantage of this detection scheme is the lifetime of the D state. We report an experimental value for this lifetime and discuss its implication for future measurements of the e-edm. [Preview Abstract] |
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R1.00146: Progress toward probing the electron electric dipole moment using the PbF molecule: The effect of the Geometric Phase on PbF Molecules Confined by a Stark-Gravitational Trap Milinda Rupasinghe, Neil Shafer-Ray The lead fluoride molecule has many features that may prove advantageous to a measurement of the electron's electric dipole moment (the e-edm.) Among these features is large (normal) dipole moment that makes it possible to confine the molecule by an anisotropic electric field. This anisotropy comes at a price: Even for the case of zero magnetic field background, an anisotropic electric field couples the angular moment of center-of-mass motion in the trap to the internal angular momentum of the molecule through a geometric phase effect. We introduce a simple trap design and calculate the dispersion in the quantum mechanical energy levels. This calculation indicates that sub-milliKelvin temperatures are required to achieve coherence times over a second. [Preview Abstract] |
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R1.00147: Progress toward probing the electron electric dipole moment using the PbF molecule: Measurement of hyperfine structure of the X1 state of PbF Christopher McRaven, Poopalasingam Sivakumar, Neil Shafer-Ray The lead fluoride molecule has many features that may prove advantageous to a measurement of the electron's electric dipole moment (the e-edm.) Among these features is a magnetic moment that should vanish at a critical value of electric field strength. To take advantage of this feature, we must polarize the molecule in a strong electric field. One way to do so is by driving an M=0 to |M|=1 RF transition. This is only possible if the hyperfine constants of the molecule are favorable. For some values of the hyperfine constants of the molecule, the RF transition energy will have very little dispersion with respect to electric field value. For other values, the dispersion is so drastic that polarization using RF radiation becomes difficult. We discuss and compare our preliminary measurements of hyperfine constants to previous experimental and theoretical efforts. We also show an experimental demonstration of an optical polarization scheme that is not sensitive to this transition-energy-dispersion problem. [Preview Abstract] |
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R1.00148: A Dipole in a Magnetic Field, Work, and Quantum Spin Robert J. Deissler Place an atom in a nonuniform static external magnetic field and, because of the interaction between the atom's magnetic moment and the magnetic field gradient, the atom will accelerate. An important and fundamental question, which has been neglected in the literature, is whether or not the magnetic field is doing work on the atom. It is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the atom's internal energy), whether or not it does work on the electron-spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. If the electron does have a rotational kinetic energy, which is shown to be consistent with the Dirac equation, the acceleration of a silver atom in a Stern-Gerlach experiment or the emission of a photon from an electron spin-flip can be explained without requiring the magnetic field to do work. A classical dipole (a spinning charged ball) is also studied. [1] Phys. Rev. E. \textbf{77}, 036609 (2008). [Preview Abstract] |
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