Bulletin of the American Physical Society
Joint Spring 2010 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 55, Number 3
Thursday–Saturday, March 18–20, 2010; Austin, Texas
Session J4: Atomic, Molecular, and Optical Physics II |
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Room: Robert Lee Moore Hall 5.104 |
Saturday, March 20, 2010 10:15AM - 10:27AM |
J4.00001: Multi-GeV electron acceleration driven by the Texas Petawatt laser X. Wang, D. Du, S.A. Yi, E. D'Avignon, S. Kalmykov, S. Reed, W. Henderson, P. Dong, R. Zgadzaj, G. Dyer, E. Gaul, M. Martinez, T. Ditmire, G. Shvets, M. Downer We present the preparation for high energy (multi-GeV) electron generation in underdense plasmas interacting with 1PW, 150fs Texas Petawatt laser pulses. Electron laser wakefield acceleration experiments have demonstrated that 1GeV electron beams can be produced with multi-TW class laser systems. Scaling laws and simulations have predicted that 3-10GeV electrons can be generated with a short pulse PW laser system without any external guiding mechanism. The Texas Petawatt system has an F /40 focusing geometry, which along with laser self-guiding creates a long laser plasma interaction length while still maintaining intensity above 10$^{19}$W/cm$^2$. This configuration also creates an opportunity to ``visualize'' the plasma wakefield structures using the single shot frequency-domain holography (FDH) technique. This presentation includes the Texas Petawatt laser, laser wakefield experimental setup, plasma diagnostic setup and anticipated preliminary experimental results during 2010. Particle-in-cell (PIC) simulations of laser wakefield electron acceleration and the FDH diagnostic are also presented. [Preview Abstract] |
Saturday, March 20, 2010 10:27AM - 10:39AM |
J4.00002: Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin Martin Abel, Katharine L.C. Hunt, Xiaoping Li, Lothar Frommhold The interaction-induced absorption by collisional pairs of H2 molecules is an important opacity source in the atmospheres of the outer planets and cool stars.\footnote{L. Frommhold, Collision-Induced Absorption in Gases, Cambridge University Press, Cambridge, New York, 1993 and 2006} The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H2---H2, H2---He, and H2---H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin. Laboratory measurements of interaction-induced absorption spectra by H2 pairs exist only at temperatures below 300 K. We show that our results reproduce these measurements closely so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures. This work has been supported in part by the National Science Foundation through Grants AST-0709106 and AST-0708496. [Preview Abstract] |
Saturday, March 20, 2010 10:39AM - 10:51AM |
J4.00003: Raman Response of Acetonitrile and Cyclohexane in the Deep Ultra-Violet Charles Manka, Robert Lunsford, Sergei Nikitin, Nagapratima Kunapareddy We present the Raman spectral response of the common solvents Acetonitrile and Cyclohexane. These are transparent liquids that provide excellent Raman spectra useful for calibration both in wavenumber and cross section of particular lines. Spectra were obtained with the NRL SWOrRD system which provided selected excitation wavelengths from 210 to 300 nm with approximately 2 nm separation. Resonant and preresonant response is analyzed with respect to electronic transitions in the vacuum ultra-violet. [Preview Abstract] |
Saturday, March 20, 2010 10:51AM - 11:03AM |
J4.00004: Using the Feynman-Kac Path Integral Method in Computing Eigenvalues for Hydrogenic Quantum Systems J.M. Rejcek, N.G. Fazleev The Feynman-Kac path integral method is applied to several hydrogenic quantum systems for the purpose of evaluating ground state eigenvalues. These are computed by random walk simulations on a discrete grid. The systems studied include free hydrogen, hydrogen in a confined spherical well and an antiproton and electron confined to the same spherical well. In addition, a method using symmetry is presented that allows higher order eigenstates to be computed. The method provides exact values in the limit of infinitesimal step size and infinite time for the lowest eigenstates. [Preview Abstract] |
Saturday, March 20, 2010 11:03AM - 11:15AM |
J4.00005: Chaotic scattering in a molecular system Alex Barr, Kyungsun Na, Linda Reichl, Christof Jung We examine the classical scattering dynamics of a chlorine atom interacting with an HO molecule using a two-dimensional model in which the HO bond length is held fixed. The classical phase space for this system is dominated by an unusually complicated homoclinic tangle. I will show how the fractal structure of the homoclinic tangle is encoded in all scattering functions and how this fractal structure can be easily investigated by defining a ``step number'' for each scattering trajectory. [Preview Abstract] |
Saturday, March 20, 2010 11:15AM - 11:27AM |
J4.00006: Quantum decoherence without a master equation Peter Bryant With a choice of boundary conditions for the Schr\"odinger equation, one finds asymmetric time evolution even for closed systems. When the theory is applied to open systems, standard quantum mechanics with unitary time evolution already predicts quantum decoherence. The practical result is a new framework for the treatment of open systems, in which no master equation is required. Preliminary calculations show very good quantitative agreement with experiments. [Preview Abstract] |
Saturday, March 20, 2010 11:27AM - 11:39AM |
J4.00007: Decay properties and photodetachment of the diatomic oxygen ion in a constant electric field Jin-Wook Jung, Kyungsun Na, Linda Reichl The effect of constant electric fields on the photodetachment of atomic ion has been studied experimentally and theoretically, but not much study has been done for the molecular ion. We study the effect of constant electric fields on the dynamics of molecular ion, O$_2^-$, in terms of a complex spectral decomposition of the energy Green's function for the open system. We describe the attractive interaction between the excess electron and the oxygen atoms by delta- function attractive potential wells and ignore the vibrational modes of the molecular ion to focus only on the effect of the new metastable states induced by the constant field. We study also the effect of the distance between the two delta-function potentials on the survival probability of the metastable state and discuss other applications of this model. (PRA 80, 012518(2009)) [Preview Abstract] |
Saturday, March 20, 2010 11:39AM - 11:51AM |
J4.00008: New Analytic Solutions of Schr\"{o}dinger's Equation in Time and Space Hichem Eleuch, Yuri Rostovtsev, Marlan Scully The Schr\"{o}dinger equation is a pillar of modern science. Numerous methods and techniques have been developed to find an exact or an approximate solution of the SE such as perturbation theory, variational methods, and diagram methods. One widely used approximation is the WKB method and variants. The WKB approximation has proven its efficiency to solve Schr\"{o}dinger-like equations. Nevertheless the WKB method is limited to an adiabatic potential where the variation of the potential energy at the distance of the order of the de Broglie wavelength is small in comparison to the kinetic energy. In the first part, we present an analytic solution beyond adiabatic approximation by transferring the 1D Schr\"{o}dinger equation into the Ricatti equation. Then we show that our solution is more accurate than WKB approximation. The generalization of the approach to 3D is suggested. In the second part, we present a new analytic treatment of the detuned atom-field interaction beyond the rotating wave approximation; we find a new approximate but very accurate analytic solution for population transfer. Finally the connection between the two parts will be discussed. [Preview Abstract] |
Saturday, March 20, 2010 11:51AM - 12:03PM |
J4.00009: A Newtonian Model of the Hydrogen Atom James Espinosa, James Woodyard Classical physics was deemed useless in atomic physics in the early 1900's by the vast majority of the physics community. There were multiple problems that were believed to be insoluble, such as blackbody radiation and the photoelectric and Compton effects. Another outstanding problem had been the explanation of atomic spectra. By the 1920's, a very powerful theory called quantum mechanics was created which explained all atomic experiments. Nevertheless, a few physicists, most notably Albert Einstein, rejected this theory on the grounds that it did not give a complete description of the microscopic world. Another more radical view held by Walter Ritz is that Newtonian physics is applicable to all of atomic physics. Over the last couple of years, we have presented classical explanations of many of the ``insoluble'' problems given by textbooks. We will present a model of the hydrogen atom that stays within the framework of Newton. Using only the assumption that the stable building blocks of matter are the electron, positron, and neutrino, we will deduce the following results from our model: orbital stability, line spectra, and scattering cross sections for electrons and protons. We will also qualitatively demonstrate how to explain the lifetime of excited states. [Preview Abstract] |
Saturday, March 20, 2010 12:03PM - 12:15PM |
J4.00010: Improvements in LabVIEW Control of BiasDACs at ATRAP Monica Lacy The primary goal of the ATRAP project at CERN is the formation of antihydrogen atoms; as part of this process, positrons are cooled, controlled and focused by passage through a series of electromagnets, and introduced into a nested Penning-Ioffe trap, where some of them combine with antiprotons to form atoms of antihydrogen. Positron cooling is controlled by LabVIEW, a graphical programming application that allows interface with multiple sensors and power supplies that control and monitor the electromagnets. A major project undertaken at ATRAP this summer was the transfer of voltage control for ten of the electromagnets to individual biasDACs (digital-to-analog boards), ensuring that the accumulation process continues independently of LabVIEW and its possible timing delays. An overview of the LabVIEW-based communication protocol for biasDACs and the process of biasDAC programming, which is expected to increase positron-antiproton interactions at ATRAP, will be presented. [Preview Abstract] |
Saturday, March 20, 2010 12:15PM - 12:27PM |
J4.00011: Supersonic expansion of molecular oxygen Jesus Perez-Rios, Massimiliano Bartolomei, Jose Campos-Martinez, Marta Isabel Hernandez, Guzman Tejeda, Jose Maria Fernandez, Salvador Montero Supersonic jets are gas dynamic quasi-universal structures showing a wealth of features combining laminar and turbulent flow, relaxation effects, shock waves, vortices, slip effects, and condensation, spanning a wide range of densities, temperatures, chemical species, and Kn numbers. In the supersonic expansion exists a zone between the nozzle and the shock wave, called the zone of silence. We apply the Raman spectroscopy in this zone to obtain the experimental number density and the population of the rotational levels. This method has a high special resolution ($<$5$\mu $m) and high-sensitivity spectroscopy ($<$photon/sec). [Preview Abstract] |
Saturday, March 20, 2010 12:27PM - 12:39PM |
J4.00012: Exploring Quantum Control Landscapes with Gun and Camera Herschel Rabitz Seeking effective control over quantum phenomena entails a search over the control landscape. The landscape is defined as the observable objective as a function of the control, typically a shaped laser pulse. The topology and features of the quantum control landscapes greatly influences the quality of the achieved controls and the efficiency of finding effective controls over quantum phenomena. Although the nature of an optimal control is highly system specific, surprisingly the landscape topology is generic for all quantum systems satisfying some basic assumptions. The background leading to the analysis of quantum control landscapes will be discussed, including relevant experimental and theoretical research. The broader physical consequences of these findings will also be considered. [Preview Abstract] |
Saturday, March 20, 2010 12:39PM - 12:51PM |
J4.00013: Modeling energy states of lithium dimers with the Born-Oppenheimer approximation Collin Lueck To obtain energy eigenstates of a two-atom system, it is necessary to separate the wavefunction of the system into nuclear and electronic components. In an adiabatic approximation, the nuclear component is a function of internuclear distance, and the electronic component is a function of electron-nuclear distance. When this approximation is used with the Numerov numerical method for plotting wavefunctions and a Distributed Approximating Function for finding energy eigenstates, it allows for plotting the energies of uncoupled states. However, more elegant and accurate solutions exist. Using a diabatic approximation, in which the wavefunctions of the nuclei are functions of the nuclear separation as well as parametric functions of the electronic motion, much more accurate energy eigenvalues are obtained. This method, when combined with a function to prevent crossings of the energy eigenstates using Clebsch-Gorden coefficients, yields a much more realistic energy plot and a deeper understanding of the two-atom system. [Preview Abstract] |
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