Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session H5: Atomic Spectroscopy II |
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Chair: Alexander Kramida, National Institute of Standards and Technology Room: Fairfield |
Wednesday, June 10, 2015 10:30AM - 10:42AM |
H5.00001: Measurement of the enhancement of the radiative decay of atoms near an optical nanofiber P. Solano, J.A. Grover, L.A. Orozco, S.L. Rolston, H.J. Carmichael The spontaneous decay rate of an atom near a dielectric is modified by the induced dipole and by a change in the modes of the vacuum electromagnetic field. This decay rate directly determines the coupling strength between an atom and the guided mode of a waveguide. We measure the spontaneous decay rate of the $5P_{3/2}$ state in $^{87}$Rb atoms near a silica optical nanofiber with a diameter of 500 nm that allows only the fundamental $HE_{11}$ mode at 780 nm. We excite a cloud of cold atoms with short, near-resonant laser pulses and use time-correlated single photon counting to directly measure the spontaneous emission into free space and into the nanofiber guided mode. Comparing the two decay constants yields a $\sim4\%$ enhancement due to the nanofiber, consistent with theory. [Preview Abstract] |
Wednesday, June 10, 2015 10:42AM - 10:54AM |
H5.00002: Diffraction using laser-driven broadband electron wave packets Junliang Xu, Cosmin I. Blaga, Kaikai Zhang, Yu Hang Lai, C.D. Lin, Terry A. Miller, Pierre Agostini, Louis F. DiMauro Directly monitoring atomic motion during a molecular transformation with atomic-scale spatio-temporal resolution is a frontier of ultrafast optical science and physical chemistry. Here we provide the foundation for a new imaging method, fixed-angle broadband laser-induced electron scattering, based on structural retrieval by direct one-dimensional Fourier transform of a photoelectron energy distribution observed along the polarization direction of an intense ultrafast light pulse. The approach exploits the scattering of a broadband wave packet created by strong-field tunnel ionization to self-interrogate the molecular structure with picometer spatial resolution and bond specificity. With its inherent femtosecond resolution, combining our technique with molecular alignment can, in principle, provide the basis for time-resolved tomography for multi-dimensional transient structural determination. [Preview Abstract] |
Wednesday, June 10, 2015 10:54AM - 11:06AM |
H5.00003: Accelerating K-Alpha Resonance Fluorescence Via Monochromatic X-Ray Beams And Comparison With LCLS-XFEL Anil Pradhan, Sultana Nahar, Sara Lim The presence of K-alpha resonances below the K-edge has been studied theoretically for high-Z (Fe, Pt, Au) and low-Z (Al, Ti, Cu) atoms [1], and recently observed experimentally at the LCLS x-ray free-electron laser facility in ``warm dense matter'' [2]. We present a mechanism for possible enhancement of the ``Auger cycle'' by employing a twin-beam monochromatic x-ray beams setup [3]. We extend the theoretical formulation to construct a detailed radiative-cascade model using atomic rates computed using atomic structure and R-matrix codes. We also report preliminary results on K-alpha resonance fluorescence from experiments at the European Synchrotron Research Facility using a tungsten target. In addition, we describe a simple Broadband-to-Monchromatic (B2M) x-ray conversion device for potential use in monochromatic K-alpha imaging and other applications [4].\\[4pt] [1] Pradhan et al., J. Phys. Chem. A. 113 45 12356 (2009); Nahar et al., Can. J. Phys. 89 5 483 (2011).\\[0pt] [2] S.M. Vinko et al., Nature 482 7383 59 (2012).\\[0pt] [3] S.N. Nahar and A.K. Pradhan, J. Quant. Spectrosc. Radiat. Transfer (in press).\\[0pt] [4] S.N. Lim, PhD Thesis, Ohio State University, 2014. [Preview Abstract] |
Wednesday, June 10, 2015 11:06AM - 11:18AM |
H5.00004: Structured photoionization continuum of cesium vapor Goran Pichler, Yacoub Makdisi, Jahja Kokaj, Nicky Thomas, Joseph Mathew We studied absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at temperature of about 450 $^{\circ}$C. This enabled the overheating of cesium dimers which almost disappeared at a temperature of 900 $^{\circ}$C leaving pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground Cs$_{2}$ molecule to the doubly excited Cs$_{2}^{\mathrm{\ast \ast }}$ molecule located above the molecular ionization limit Cs$_{2}^{+}$. The corresponding potential curves are subjected to a mutual interactions and autoionization. [Preview Abstract] |
Wednesday, June 10, 2015 11:18AM - 11:30AM |
H5.00005: Enhanced absorption and Autler-Townes splitting of electromagnetically induced transparency Matthew Simons, Christopher Holloway, Joshua Gordon, David Anderson, Stephanie Miller, Andrew Schwarzkopf, Nithiwadee Thaicharoen, Georg Raithel We study the dependence of the Autler-Townes splitting of electromagnetically induced transparency (EIT) in $^{85}Rb$ from an applied RF electric field on pump and probe laser power. The probe is tuned to the $5S_{1/2} \rightarrow 5P_{3/2}$ transition, and the pump is tuned to a $5P_{3/2} \rightarrow$ Rydberg transition to set up EIT in the probe transmission. The applied RF field is resonant with a neighboring Rydberg state transition, causing frequency splitting of the EIT signal. The splitting is proportional to the magnitude of the RF field, which is the basis for Rydberg atom EIT-based RF field probes. Increased laser power tends to broaden the transitions and low laser power reduces the overall signal. However, low probe laser power can allow enhanced absorption of the probe. This enhanced absorption can increase the ability to detect weak RF fields by improving the visibility of the EIT signal. This has applications to improving the sensitivity of Rydberg atom EIT-based RF field probes. [Preview Abstract] |
Wednesday, June 10, 2015 11:30AM - 11:42AM |
H5.00006: Hydrogen \textit{ Balmer} Series Self-Absorption Measurement in Laser-Induced Air Plasma Ghaneshwar Gautam, Christian Parigger In experimental studies of laser-induced plasma, we use focused Nd:YAG laser radiation to generate optical breakdown in laboratory air. A \textit{Czerny-Turner} type spectrometer and an ICCD camera are utilized to record spatially and temporally resolved spectra. Time-resolved spectroscopy methods are employed to record plasma dynamics for various time delays in the range of 0.300 microsecond to typically 10 microsecond after plasma initiation. Early plasma emission spectra reveal hydrogen alpha and ionized nitrogen lines for time delays larger than 0.3 microsecond, the hydrogen beta line emerges from the free-electron background radiation later in the plasma decay for time delays in excess of 1 microsecond. The self-absorption analyses include comparisons of recorded data without and with the use of a doubling mirror. The extent of self-absorption of the hydrogen \textit{Balmer} series is investigated for various time delays from plasma generation. There are indications of self-absorption of hydrogen alpha by comparison with ionized nitrogen lines at a time delay of 0.3 microsecond. For subsequent time delays, self-absorption effects on line-widths are hardly noticeable, despite the fact of the apparent line-shape distortions. Of interest are comparisons of inferred electron densities from hydrogen alpha and hydrogen beta lines as the plasma decays, including assessments of spatial variation of electron density. [Preview Abstract] |
Wednesday, June 10, 2015 11:42AM - 11:54AM |
H5.00007: Positron Annihilation 3-D Momentum Spectrometry by Synchronous 2D-ACAR and DBAR Larry W. Burggraf, Angelo M. Bonavita, Christopher S. Williams, Stefan B. Fagan-Kelly, Stephen M. Jimenez A positron annihilation spectroscopy system capable of determining 3D electron-positron (e$^{-}$-e$^{+})$ momentum densities has been constructed and tested. In this technique two opposed HPGe strip detectors measure angular coincidence of annihilation radiation (ACAR) and Doppler broadening of annihilation radiation (DBAR) in coincidence to produce 3D momentum datasets in which the parallel momentum component obtained from the DBAR measurement can be selected for annihilation events that possess a particular perpendicular momentum component observed in the 2D ACAR spectrum. A true 3D momentum distribution can also be produced. Measurement of 3-D momentum spectra in oxide materials has been demonstrated including O-atom defects in 6H SiC and silver atom substitution in lithium tetraborate crystals. Integration of the 3-D momentum spectrometer with a slow positron beam for future surface resonant annihilation spectrometry measurements will be described. [Preview Abstract] |
Wednesday, June 10, 2015 11:54AM - 12:06PM |
H5.00008: Self Absorption of 394.4 and 396.15 nm Aluminum Transitions in Laser-Induced Plasma David Surmick, Christian Parigger Transient plasma produced from a pulsed laser source is an advantageous laboratory method for studying Stark broadening parameters of atomic spectra through comparisons to known metrics such as Stark line widths and shifts of hydrogen. In performing such studies one aims to experimentally determine line width and shift parameters which requires independent measures of the electron number density and temperature. Such measurements are often complicated by non-equilibrium conditions including self absorption effects which cause distorted and broadened atomic line shapes. In this work, we seek to quantify the measured spatial and temporal dependence of two aluminum atomic transitions at 394.4 and 396.15 nm from the plasma following laser-induced breakdown near an aluminum alloy target. The self absorption effects are addressed by measuring the aluminum spectra with and without a duplicating mirror. The reflected plasma radiation is propagated through the plasma and is also imaged onto the spectrometer slit and detector arrangement. Initial measurements of the electron number density from the Al transitions indicate that self absorption behavior between the two lines may not be the same. The electron number density is found to be 1.92 $\pm$ 0.21 $\times$ 10$^{18}$ cm$^{-3}$ and 3.25 $\pm$ 0.44 $\times$ 10$^{18}$ cm$^{-3}$ for the 394.4 and 396.15 nm lines, respectively, from the primarily Stark broadened line profiles at a time delay of 0.3 $\mu $s following laser-induced optical breakdown accomplished with nanosecond pulsed, Q-switched Nd:YAG laser radiation. [Preview Abstract] |
Wednesday, June 10, 2015 12:06PM - 12:18PM |
H5.00009: Four -body calculation of the 2p level shift in antikaonic helium $\bar{K}3$He atom Shalva Tsiklauri, Joshua Tenon The strong interaction of charged antikaons (K -) with nucleons and nuclei in the low-energy is a intriguing subject matter. The antikaon plays an unusual role in nuclear physics due to the strong attraction antikaon-nucleon which is a key question for possible kaonic nuclear bound states. Low-lying energy levels of kaonic atoms are shifted from their pure electromagnetic values and widened due to the strong interaction between the antikaon and nucleon. The level shift and width of the kaonic atoms can be determined by x-ray spectroscopy.The X-ray measurements of $\bar{K}$He atoms introduced inconsistency between theory and experiment both in the shift and width of the $\bar{K}$He 2$p $state. The average of the shift was large $\sim $40 eV, while a majority of theoretical calculations suggested very small shift below 1 eV . This significant disagreement between the experimental results and the theoretical calculations is known as the ``kaonic helium puzzle.'' We suggest a new theoretical analysis of the four-body antikaonic $^{3}$He in the framework of the method of hyperspherical harmonics (HH) for solving four body Schrodinger equations. This is the first time when the HH microscopic method is applied to study kaonic helium. [Preview Abstract] |
Wednesday, June 10, 2015 12:18PM - 12:30PM |
H5.00010: Spectral Description of Multi-Photon Processes in Quantized Many-Electron Systems Based on a Reduced-Density-Matrix Approach Verne Jacobs The frequency-dependent transition rates for multi-photon processes in quantized many-electron systems are evaluated using a reduced-density-matrix approach. A fundamental foundation, based on quantum electrodynamics, is provided for systematic spectral simulations for electromagnetic interactions in quantized many-electron systems, including atomic, molecular, and solid-state systems. A perturbation expansion of the frequency-domain Liouville-space self-energy operator is employed in detailed evaluations of the spectral-line shapes. The self-energy contributions associated with environmental electron-photon and electron-phonon interactions are systematically taken into account. Detailed evaluations have been carried out for the spectral-line widths and shifts in the diagonal-resolvent, lowest order (Born), and short-memory-time (Markov) approximations. [Preview Abstract] |
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