Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session H05: Focus Session: AMO Science with Free Electron Lasers |
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Chair: Daniel Rolles, Kansas State University Room: Grand E |
Wednesday, May 30, 2018 8:00AM - 8:30AM |
H05.00001: Ultrafast electronic and nuclear dynamics induced by intense, ultrashort XFEL pulses. Invited Speaker: Kiyoshi Ueda In 2012, SACLA, an XFEL in Japan, started user operation. We set up a program to investigate ultrafast electronic and nuclear dynamics in atoms, molecules and clusters induced by intense, ultrashort pulses generated by SACLA. At photon energy of 5.0-5.5 keV, we found an evidence for occurrence of deep inner-shell ionization and sequential electronic decay cycles repeated multiple times in the xenon atom within 10 fs pulse duration. The results for momentum-resolved multiple ion coincidence study on iodine-contained organic molecules illustrated that the charges are produced by the cycles of deep inner-shell ionization of the iodine atom and sequential electronic decay and spread over the entire molecule within 10 fs, leading to Coulomb explosion. The measured momentum distributions and correlations are well reproduced by MD simulations. The results for electron spectroscopy on rare gas clusters, with help of theoretical calculations, illustrated that a nanoplasma is formed by the XFEL pulse in tens of fs, and continuous thermal emission from the plasma occurs in ps. To probe these XFEL-induced ultrafast reactions in atoms, molecules, and clusters in real time, we carried out also XFEL pump-NIR probe experiments. The latest results will be shown and discussed. [Preview Abstract] |
Wednesday, May 30, 2018 8:30AM - 9:00AM |
H05.00002: Time-Resolved Photoionization and Fragmentation Dynamics of Fullerenes Studied with the Linac Coherent Light Source Free Electron Laser (FEL) Invited Speaker: Nora Berrah Time-resolved photo-induced responses of fullerenes subject to femtosecond free electron laser (FEL) x-ray ionization provide critical understanding of the fundamental mechanisms that drive the conversion of photons into chemical and kinetic energy on ultrafast timescales. We have measured and predicted the critical change in the behavior of fullerenes ionization using photons at the energy of 640 eV with 20 fs pulse duration. The experiment used the LCLS fresh slice x-ray pump and x-ray probe technique. The time-resolved experiment is interpreted with Molecular Dynamics Modeling to expose, from a fundamental point of view, the physical and chemical processes and their time evolution as well as provide information on the radiation damage relevant to bio-molecules. [Preview Abstract] |
Wednesday, May 30, 2018 9:00AM - 9:12AM |
H05.00003: XUV-Assisted High-Order Harmonic Generation Shashank Pathak, Jan Tross, Adam Summers, Daniel Rolles, Carlos Trallero, Dimitrios Rompotis, Benjamin Erk, Christopher Passow, Bastian Manschwetus, Sadia Bari, Rebecca Boll, Patrik Grychtol We report on the high-order harmonics generation (HHG) by a near-infrared (NIR) laser pulse in the presence of an extreme ultraviolet (XUV) field. The experiments were performed using the free-electron laser (FEL) in Hamburg (FLASH), Germany. Previous theoretical studies predict an enhancement of the HHG yield when XUV and NIR fields are combined [1]. In our experiments, we were able to observe such an enhancement, albeit very small, in the HHG yield of argon and krypton at different XUV wavelengths. Furthermore, we observe a strong decrease in the HHG yield when the XUV pulse precedes the NIR. [1] C. Buth, M.C. Kohler, J. Ullrich, C.H. Keitel, Opt. Lett. \textbf{36}, 3530--3532 (2011) [Preview Abstract] |
Wednesday, May 30, 2018 9:12AM - 9:24AM |
H05.00004: Quantum coherent control of the photoelectron angular distribution in bichromatic-field ionization. Klaus Bartschat, Nicolas Douguet, Elena V. Gryzlova, Alexei N. Grum-Grzhimailo, Ekaterina I. Staroselskaya We investigate the coherent control of the photoelectron angular distribution (PAD) in bichromatic atomic ionization. Practical issues, such as the role of the fine-structure splitting, the pulse length, and the intensity, are discussed. We employ time-dependent and stationary perturbation theory, and we also solve the time-dependent Schr\"odinger equation in a single-active electron model. As a specific example, we consider atomic neon, for which a recent experiment [1] used one of the $(2p^5 4s)$ states with total electronic angular momentum $J=1$ as the intermediate state in simultaneous two-photon excitation by the fundamental and one-photon ionization by the second harmonic of the seeded free-electron laser FERMI [2]. Coherent control of the PAD was achieved by controlling the time delay, corresponding to the relative phase, between the fundamental and the second harmonic to a precision of 3.1 attoseconds. We also investigate the contribution of the nonresonant two-photon process and its potentially constructive or destructive role for quantum coherent control. [1] K.~C.~Prince {\it et al.}, Nature Photonics~{\bf 10} (2016) 176. [2]~https://www.elettra.trieste.it/lightsources/fermi.html [Preview Abstract] |
Wednesday, May 30, 2018 9:24AM - 9:36AM |
H05.00005: X-ray emission in Clusters Exposed to Intense X-ray Free-electron Laser (XFEL) Pulses Phay Ho, Chris Knight, Linda Young, Christoph Bostedt We present a theoretical study in the effects of non-linear x-ray ionization dynamics on x-ray emission processes in clusters in intense XFEL pulses.~ We employ Monte-Carlo/Molecular Dynamics calculations to investigate the x-ray processes as a function of pulse parameters (photon energy, intensity and pulse duration) and cluster shape.~ We found that the nanosized Ar cluster x-ray emission spectrum in the high-intensity (\textgreater 10$^{\mathrm{20\thinspace }}$W/cm$^{\mathrm{2}})$ pulse is very different from the Ar atom spectrum. Most notably, the Ar cluster spectrum depicts stronger fluorescence lines for K$_{\mathrm{\alpha }}$ and K$^{\mathrm{h}}_{\mathrm{\alpha }}$. Moreover, their satellites which are negligible in the atomic spectrum, become very pronounced in the Ar cluster spectrum. Our analysis shows that recombination processes are an important contribution to these fluorescence features, in which recombination processes enable additional pathways to reach the required electronic configurations for fluorescence transitions. Interestingly, we found that the x-ray emission profile can be modulated by changing the shape of cluster. [Preview Abstract] |
Wednesday, May 30, 2018 9:36AM - 9:48AM |
H05.00006: Anisotropic evaporation of a large nanoplasma Camila Bacellar, Christoph Bostedt, Andrey Vilesov, Oliver Gessner Laser-induced plasma dynamics in $\approx$600~nm sized helium droplets are monitored by femtosecond time-resolved X-ray coherent diffractive imaging at the Linac Coherent Light Source (LCLS). An anisotropic, 20~nm wide softened surface region is established within 300~fs. At longer timescales, the width of this region remains largely constant but the dense plasma core diameter shrinks at average rates of 140~nm/ps along and 70~nm/ps perpendicular to the laser polarization. An anisotropic plasma evaporation model reproduces the key experimental observations and connects the findings of previous studies on small nanoscale systems with the dynamics of self-contained plasmas approaching micron scales. The model is supported by angle-resolved ion kinetic energy distributions recorded in coincidence with the X-ray diffraction patterns. [Preview Abstract] |
Wednesday, May 30, 2018 9:48AM - 10:00AM |
H05.00007: Radiation damage dynamics of light and heavy atoms of biological significance in Hartree-Fock and Kohn-Sham models Alexander Kozlov, Harry M. Quiney Simulations of radiation damage in single molecule imaging using X-ray free electron laser use atomic rates calculated in the lowest order \cite{Kengo2012, Ho2017}. We investigate the difference in ionization dynamics predicted by Hartree-Fock and Kohn-Sham methods for light and heavy elements of biological significance. These methods produce very similar results for light atoms in short and bright pulses. For heavy atoms and light atoms in pulses with smaller peak intensity the predictions of the models may differ considerably. The presented analysis allows us to predict if two approaches will produce similar results for a given atom and a pulse with specified parameters. We demonstrate the sensitivity of the charge state dynamics to Auger rates and discuss the choice of effective potential and gauge for fluorescence and photoionization processes. \begin{bibliography}{10} \bibitem{Kengo2012} K.~Moribayashi, \newblock X-Ray Spectroscopy (2012). \bibitem{Ho2017} P.~J.~Ho and C.~Knight, \newblock J. Phys. B. {\bf 50}, 104003 (2017). \end{bibliography} [Preview Abstract] |
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