Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session U7: Physics with Ultraintense Lasers and Light Sources |
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Chair: Itzik Ben-Ithzak, Kansas State University Room: Terrace |
Friday, June 8, 2012 10:30AM - 10:42AM |
U7.00001: X-ray resonance fluorescence and Rabi flopping for ultrafast and ultraintense pulses Stefano M. Cavaletto, Zolt\'{a}n Harman, Christoph H. Keitel, Christian Buth, Elliot P. Kanter, Linda Young, Stephen H. Southworth Resonance fluorescence is scattering of photons off atoms and molecules driven by a near-resonant external electric field; it is a cornerstone of spectroscopy and quantum optics. For intense x rays from existing and upcoming x-ray free electron lasers (FELs) such as the Linac Coherent Light Source (LCLS) in Menlo Park, California, USA, the cyclic excitation and decay of a core electron (Rabi flopping) can compete with spontaneous core-hole decay. We develop a two-level description of x-ray resonance fluorescence and exemplify it for neon cations strongly driven by LCLS light tuned to the $1s\,2p^{-1}\rightarrow 1s^{-1}\,2p$ transition at 848 eV. We compute the time-dependent spectrum of resonance fluorescence in order to study the coherent and fundamentally nonlinear process of Rabi flopping at x-ray frequencies. We predict resonance fluorescence spectra for two different scenarios: first, chaotic pulses generated at present-day LCLS and, second, Gaussian pulses which will become available soon with self-seeding techniques. In the latter case, as an example of the exciting opportunities deriving from the use of seeding methods, we predict a clear signature of Rabi flopping in the spectrum of resonance fluorescence. [Preview Abstract] |
Friday, June 8, 2012 10:42AM - 10:54AM |
U7.00002: Femtosecond time-resolved x-ray photoelectron spectroscopy studies of charge transfer dynamics in novel photovoltaic systems Oliver Gessner, Andrey Shavorskiy, Katrin Siefermann, Daniel Slaughter, Felix Sturm, Fabian Weise, Matthew Strader, Hana Cho, Ming-Fu Lin, Travis Wright, Jinghua Guo, Hendrik Bluhm, Robert Schoenlein, Ali Belkacem, Daniel Neumark, Stephen Leone, Amy Cordones, Josh Vura-Weis, Sheraz Gul, Jin Zhang, Dennis Nordlund, Hirohito Ogasawara, Anders Nilsson, Martin Beye, Nils Huse Interfacial charge transfer dynamics in dye-sensitized semiconductor films are studied by femtosecond time-resolved x-ray photoelectron spectroscopy. The experiments performed at the Linac Coherent Light Source demonstrate the potential of time-domain inner-shell photoionization studies to monitor charge migration in complex interfacial systems with femtosecond time resolution, chemical sensitivity and atomic specificity. Using this new technique, the transient oxidation state of N3 dye molecules adsorbed to nanocrystalline ZnO is monitored with unprecedented site selectivity, providing an upper bound for the interfacial electron-hole recombination rate. [Preview Abstract] |
Friday, June 8, 2012 10:54AM - 11:06AM |
U7.00003: Electron-positron-photon cascades in the strong laser field Maxim Legkov, Alexander Fedotov At nearest future several ambitious projects (such as ELI and HiPER) may provide laser filed intensity up to 10$^{23}$--10$^{24}$ W/cm$^{2}$. In such strong fields quantum effects are essential. The most important among them is production of QED cascades. In this paper external field intensity is considered as ultra-relativistic but subcritical. Using a model of two colliding counter-propagating laser beams it was shown that the number of particles during the process is growing exponentially in time. This leads to vast formation of electron-positron-photon plasma. According to numerical simulations, this plasma quickly absorbs an essential part of the energy of the laser field thus leading to its depletion. Numerical simulation has been also performed for a case of high-energetic particle and laser beam collision. Probability rates of direct and recombination processes have been theoretically studied. Under some conditions, recombination may come into play and suppress cascade development. Using approximation of radiation in forward direction, system of kinetic equations, which describes plasma evaluation, was constructed. According to qualitative estimations based on kinetic equations, it was shown that recombination processes can be neglected for optical frequencies range of external field. [Preview Abstract] |
Friday, June 8, 2012 11:06AM - 11:18AM |
U7.00004: Tracing nuclear wave-packet dynamics in diatomic molecules with XUV pump- and probe- pulses M. Magrakvelidze, O. Herrwerth, Y.H. Jiang, A. Rudenko, M. Kurka, L. Foucar, K.U. K\"{u}hnel, M. K\"{u}bel, N.G. Johnson, C.D. Schr\"{o}ter, S. D\"{u}sterer, R. Treusch, M. Lezius, I. Ben-Itzhak, R. Moshammer, J. Ullrich, M.F. Kling, U. Thumm We traced the femtosecond nuclear wave-packet dynamics in ionic states of oxygen and nitrogen diatomic molecules employing 38 eV XUV pump and probe at the \underline {F}ree Electron \underline {Las}er in \underline {H}amburg (FLASH).\footnote{Y. H. Jiang \textit{et al.}, PRA \textbf{82}, 041403(R) (2010).} The nuclear dynamics is monitored via the detection of coincident ionic fragments using a reaction microscope and a split-mirror setup to generate the pump and probe pulses. By comparing measured kinetic-energy-release (KER) spectra with classical and quantum-mechanical simulations,\footnote{I. A. Bocharova \textit{et al.}, PRA \textbf{83}, 013417 (2011)} we identified electronic states of the molecular ions that are populated by ionization of the neutral molecule. The comparison of measured KER spectra for specific fragment-charge states allows assessing the relevance of specific dissociation paths. [Preview Abstract] |
Friday, June 8, 2012 11:18AM - 11:30AM |
U7.00005: Laser-generated proton bunches from chirped laser-plasma interaction Benjamin Galow, Yousef Salamin, Tatyana Liseykina, Zoltan Harman, Jian-Xing Li, Christoph Keitel Detailed single- and many-particle calculations are carried out for the acceleration of protons employing linearly-polarized plane-wave and tightly-focused chirped laser pulses of several ten to several hundred femtosecond durations, petawatt peak powers and relativistic peak intensities of the order of $10^{21}-10^{22}$~W/cm$^2$ [1,2]. Analytic and numerical methods of calculation are used in the single-particle cases (in vacuum), and particle-in-cell (pic) simulations (under-dense plasma) are employed in the many-particle investigations, without and with electromagnetic particle-particle interactions, respectively. Feasibility of generating ultra-intense ($10^7$ particles per bunch) and phase-space collimated beams of protons is demonstrated. Interaction of the protons with the quasi-static part of the laser pulse allows the particles to gain sufficient kinetic energy (around $250$ MeV) required for such applications as hadron cancer therapy.\\[4pt] [1] B.~J.~Galow, Y.~I.~Salamin, T.~V.~Liseykina, Z.~Harman, and C.~H.~Keitel, Phys. Rev. Lett. {\bf 107}, 185002 (2011)\\[0pt] [2] Y.~I.~Salamin, J.-X.~Li, B.~J.~Galow, Z.~Harman, and C.~H.~Keitel, submitted (2012) [Preview Abstract] |
Friday, June 8, 2012 11:30AM - 11:42AM |
U7.00006: Controlling Auger decay with electromagnetically induced transparency for x rays Antonio Picon, Gilles Doumy, Stephen Southworth, Linda Young, Christian Buth The emerging x-ray free electron lasers (FELs) such as the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory can reach very high intensities and ultrashort pulse durations. We analyze how to control Auger decay using a secondary intense near-infrared (NIR) laser with electromagnetically induced transparency for x rays. A three-level $\Lambda$-type model is used, where a core electron is coupled to a Rydberg state by the x rays while the NIR pulse couples the Rydberg states among each other. We use the model to predict the Auger electron spectrum of a neon atom and thus enhance our understanding and control of electron correlations. This work opens up new prospects to study and control the nonlinear interaction of ultraintense and ultrashort x rays with atoms. [Preview Abstract] |
Friday, June 8, 2012 11:42AM - 11:54AM |
U7.00007: Effect of wave-function localization on the time delay in photoemission from surfaces Uwe Thumm, Chanh-hua Zhang We investigated streaking time delays in the photoemission from a solid model surface as a function of the degree of localization of the initial-state wave functions [1]. We consider a 1D slab with lattice constant $a_{latt}$ of attractive Gaussian-shaped core potentials of width \textit{$\sigma $}. The parameter \textit{$\sigma $ / a}$_{latt}$ thus controls the localization of the electronic eigenfunctions. Small values of \textit{$\sigma $ / a}$_{latt} \quad <<$1 yield lattice eigenfunctions that consist of localized atomic wave functions modulated by a ``Bloch-envelope'' function, while the eigenfunctions become delocalized for larger values of \textit{$\sigma $ / a}$_{latt}$ $>$ 0$.$4. From calculated photoemission spectra we deduced a characteristic \textit{bimodal }shape of the band-averaged photoemission time delay: as the slab eigenfunctions become increasingly delocalized, the time delay quickly decreases near \textit{$\sigma $ / a}$_{latt}$ = 0$.$3. This change in wave-function localization facilitates the interpretation of a recently measured apparent relative time delay [2] between the photoemission from core and conduction-band levels of a tungsten surface [3]. \\[4pt] [1] C.-H. Zhang and U. Thumm, Phys. Rev. A \textbf{84}, 065403 (2011).\\[0pt] [2] C.-H. Zhang and U. Thumm, Phys. Rev. A \textbf{84}, 033401 (2011).\\[0pt] [3] C.-H. Zhang and U. Thumm , Phys. Rev. Lett. 102, 123601 (2009). [Preview Abstract] |
Friday, June 8, 2012 11:54AM - 12:06PM |
U7.00008: Non-linear Compton Scattering in Short Laser Pulses Katarzyna Krajewska, Jerzy Kami\'nski The generation of short X-ray laser pulses attracts a great deal of attention. One of mechanisms to achieve this goal is the non-linear Compton scattering at very high laser powers. The majority of previous works on the non-linear Compton scattering have been devoted to the case when the incident laser field is treated as a monochromatic plane wave. There is, however, recent interest in analyzing the effect of a pulsed laser field on the non-linear Compton scattering [1-4]. We study the process for different durations of the incident laser pulse and compare it with the results for both a plane wave laser field and a laser pulse train. \\[4pt] [1] M. Boca and V. Florescu, Phys. Rev. A {\bf 80}, 053403 (2009).\\[0pt] [2] M. Boca and V. Florescu, Eur. Phys. J. D {\bf 61}, 446 (2011).\\[0pt] [3] D. Seipt and B. K\"ampfer, Phys. Rev. A {\bf 83}, 022101 (2011).\\[0pt] [4] F. Mackenroth and A. Di Piazza, Phys. Rev. A {\bf 83}, 032106 (2011). [Preview Abstract] |
Friday, June 8, 2012 12:06PM - 12:18PM |
U7.00009: Attosecond x rays from x-ray-boosted high-order harmonic generation Christian Buth, Markus C. Kohler, Feng He, Karen Z. Hatsagortsyan, Joachim Ullrich, Christoph H. Keitel We theoretically examine high-order harmonic generation~(HHG) by an intense near-infrared~(\textsc{nir}) laser in combination with intense x~rays from a free electron laser such as the Linac Coherent Light Source (LCLS) at SLAC. The x~rays are tuned above an absorption edge thus causing one-photon ionization of a tightly bound core electron. The liberated core electron is driven by the \textsc{nir}~light through the continuum; when the electric \textsc{nir}~field reverses its direction, the electron may eventually return to the cation leading to its recombination with the core hole and the emission of a high-harmonic photon that is upshifted in energy by the x-ray~photon energy. We develop a theory of this x-ray boosted HHG scenario and apply it to $1s$~electrons of neon atoms. HHG spectra are computed for LCLS pulses which are generated according to the self-amplification of spontaneous emission~(SASE) principle. A time-frequency analysis of HHG emission reveals the imprinting of the varying LCLS pulse shapes on the boosted HHG spectrum which may open up prospects for pulse diagnostic. The boosted HHG~light is used to generate a single attosecond pulse in the kiloelectronvolt regime by filtering out only the highest HHG photons close to the upshifted cutoff. [Preview Abstract] |
Friday, June 8, 2012 12:18PM - 12:30PM |
U7.00010: Correction of the relativistic factorizable expression (RKJ) for Compton scattering doubly differential cross sections L.A. LaJohn, R.H. Pratt We have derived simple analytic expressions that can be used to correct the factorizable expression for Compton scattering doubly differential cross sections (DDCS) within the relativistic impulse approximation (RIA). This relativistic factorizable expression, which we refer to as the RKJ approximation, has the nonrelativistic-like form DDCS=KJ, where K is a kinematic factor and J is the Compton profile. The advantage of RKJ is that it allows one to obtain J from observed DDCS in relativistic regimes. However RKJ breaks down for K-shell ionization of moderate to heavy atoms. The error can exceed $25\%$ for heavy atoms such as Uranium. Our correction to RKJ provides accurate Compton profiles at high energy, at least around the maxima, even for the heaviest of atoms. We explain how the formulas for the correction to RKJ can be obtained most conveniently by taking the high incident photon energy $\omega_i$ limit of the partially integrated form of the full RIA expression for DDCS and why this partially integrated form exhibits the cancellation of much of the relativistic corrections to the RKJ approximation, resulting in simple expressions that yield accurate results. We give the results of tests for the accuracy of the corrected K-shell Compton profiles for heavy atoms. [Preview Abstract] |
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