Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session H7: Focus Session: Ultrafast and Nonlinear Xray ProcessesFocus
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Chair: Gilles Doumy, Argonne National Laboratory Room: 313 |
Wednesday, June 7, 2017 10:30AM - 11:00AM |
H7.00001: Coherent Multidimensional Core Spectroscopy of Molecules with Multiple X-ray pulses Invited Speaker: Shaul Mukamel Multidimensional spectroscopy uses sequences of optical pulses to study dynamical processes in complex molecules through correlation plots involving several time delay periods. Extensions of these techniques to the x-ray regime will be discussed. Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. We demonstrate how stimulated Raman detection of an X-ray probe may be used to monitor the phase and dynamics of the nonequilibrium valence electronic state wavepacket created by e.g. photoexcitation, photoionization and Auger processes. Spectroscopy of multiplecore excitations provides a new window into electron correlations. Applications will be presented to long-range charge transfer in proteins and to excitation energy transfer in porphyrin arrays. Conical intersections (CoIn) dominate the pathways and outcomes of virtually all photophysical and photochemical molecular processes. Despite extensive experimental and theoretical effort CoIns have not been directly observed yet and the experimental evidence is being inferred from fast reaction rates and some vibrational signatures. Novel ultrafast X ray probes for these processes will be presented. Short X-ray pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn. Streaking of time-resolved photoelectron spectroscopy (TRPES) signals offers another powerful window into the joint electronic/vibrational dynamics at concial intersections. Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby manipulating the photophysical and photochemical reaction pathways. The photonic vacuum state of a localized cavity mode can be strongly mixed with the molecular degrees of freedom to create hybrid field-matter states known as polaritons. Simulations of the avoided crossing of sodium iodide in a cavity which incorporate the quantized cavity field into the nuclear wave packet dynamics will be presented. Numerical results show how the branching ratio between the covalent and ionic dissociation channels can be strongly manipulated by the optical cavity. [Preview Abstract] |
Wednesday, June 7, 2017 11:00AM - 11:12AM |
H7.00002: Pulse energy and pulse duration dependence of multi-photon ionization and fragmentation of iodomethane by ultraintense hard X-rays. X. Li, S.J. Robatjazi, D. Rolles, A. Rudenko, B. Erk, R. Boll, C. Bomme, E. Savelyev, B. Rudek, L. Foucar, Ch. Bostedt, C.S Lehmann, B. Kraessig, S.H. Southworth, L. Young, M. Bucher, T. Marchenko, M. Simon, K. Ueda, K.R. Ferguson, T. Gorkhover, R. Alonso-Mori, S. Carron, G. Williams, S. Boutet Ionization and fragmentation dynamics of iodomethane molecules (CH3I) irradiated by ultraintense 8.3 keV X-ray pulses from the Linac Coherent Light Source has been studied as a function of pulse energy and pulse duration. As intuitively expected, the measured ion charge state distributions (CSD) are very sensitive to the pulse energy. On the contrary, when varying the pulse duration from 20 to 60 fs at a fixed pulse energy, we did not observe any systematic change of the CSD, indicating that in this regime ionization level is defined by the pulse fluence rather than the intensity. The measured ion kinetic energies for a given charge state, however, exhibit the opposite trend, depending on the pulse duration and being rather insensitive to the pulse energy. We discuss underlying electronic and nuclear dynamics resulting in these observations. [Preview Abstract] |
Wednesday, June 7, 2017 11:12AM - 11:24AM |
H7.00003: X-ray and Laser-Induced Fragmentation of 2,6- and 3,5-difluroiodobenzene Utuq Ablikim, Farzaneh Ziaee, Rajesh Kushwahana, Artem Rudenko, Daniel Rolles, Cedric Bomme, Evgeny Savelyev, Hui Xiong, Nora Berrah, Timur Osipov Studying the intramolecular dynamics of complex (bio-) molecules is challenging both theoretically and experimentally. These large molecules typically exhibit multiple structural isomers, which are distinct species with different physical and chemical properties. We carried out coincidence momentum imaging experiments on gas-phase 2,6- and 3,5-difluroiodobenzene isomers, using both soft X-rays and ultrafast lasers. Using the momentum correlation between iodine and fluorine cations in three-fold coincidence channels, we can distinguish the two isomers experimentally. We also find that the majority of the many-body fragmentations happen in a two-step process, where the iodine-carbon bond is broken first and the second-step Coulomb explosion occurs when the metastable C$_{\mathrm{6}}$H$_{\mathrm{3}}$F$_{\mathrm{2}}^{\mathrm{++}}$ dication fragments into smaller ionic species. [Preview Abstract] |
Wednesday, June 7, 2017 11:24AM - 11:36AM |
H7.00004: Scattering Response of Sucrose Clusters with Intense XFEL Pulses in Water Window Phay Ho, Benedikt Benedikt Daurer, Johan Bielecki, Max Hantke, Filipe Maia, Chris Knight, Janos Hajdu, Linda Young, Christoph Bostedt We present a combined experimental and theoretical study about the effects of non-linear x-ray ionization dynamics on the scattering response of molecular clusters in the soft x-ray regime that includes and goes beyond the water window.~ Nanosized sucrose clusters were irradiated with intense XFEL pulses (photon energy from 500 to 1500 eV and pulse duration of 180 fs).~~ Surprisingly, the measured scattering signals near the oxygen K-edge in the water window are found to be substantially smaller than those at higher photon energies.~ We employ Monte-Carlo/Molecular Dynamics calculations to investigate the x-ray processes as a function of pulse parameters (photon energy, bandwidth and pulse duration) and cluster size.~ We demonstrate the important role of resonant excitation (RE) in the molecular scattering response in the water window.~ In particular, 1s -\textgreater 2p RE cycling enabled in the oxygen atom/ion provide additional ionization pathways which, combined with the long pulse duration, lead to substantial reduction in scattering power of sugar clusters for photon energies just below the oxygen K-edge. [Preview Abstract] |
Wednesday, June 7, 2017 11:36AM - 11:48AM |
H7.00005: Rotational coherence as an alternative to coincidence techniques at x-ray free electron lasers Ryan Coffee, Kareem Hegazy, Nick Hartmann, Peter Walter, Timur Osipov, Anton Lindahl, Wolfram Helml, Markus Ilchen, Andreas Galler, Jia Liu, Jens Buck, Ivan Shevchuk, Jens Viefhaus, Gregor Hartmann, Andre Knie, Philipp Demekhin, Ludger Inhester, Zheng Li, Beata Ziaja-Motyka, Nikita Medvedev, Christoph Bostedt, Renaud Guillemin, Marc Simon, Maria Novella-Piancastelli, Catalin Miron We demonstrate an alternative approach to coincidence particle detection, based on impulsive rotational Raman excitation, for molecular frame measurements at x-ray FELs. A train of 8 infrared laser pulses induces the lab-frame observable coherence. At a field-free alignment revival, we register the angle-resolved laboratory frame Auger and photo-electron spectral feature variations with the tumbling molecular body frame. The time and angle dependence of the electron emission patterns that constrain theory are amenable to large numbers of interactions per pulse and, more importantly, has no axial recoil requirement for kinematic reconstruction. We see this as a method to bypass experimental challenges at XFELs by accepting [Preview Abstract] |
Wednesday, June 7, 2017 11:48AM - 12:00PM |
H7.00006: Coherent control of the photoelectron angular distribution in short-pulse XUV ionization of neon. N. Douguet, K. Bartschat, A. N. Grum-Grzhimailo, E. V. Gryzlova, E. I. Staroselskaya Light-induced coherent control of the photoelectron angular distribution (PAD) in neon was recently achieved using the Free-Electron Laser (FEL) at FERMI [1]. To gain a better understanding of these processes, which promise a rich field of possibilities in the control of matter, we investigated two-pathway interferences in the ionization of neon induced by the fundamental and second harmonic of a femtosecond XUV pulse when either $\rm(2p^54s)^1P$~[1] or $\rm(2p^53s)^1P$~[2] are chosen as intermediate states to enhance the two-photon ionization probability. Using a time-dependent approach supported by a perturbative formalism, we analyze the effects of varying the fundamental frequency, intensity ratio between harmonics, and carrier envelope phase. Our results are compared with new experimental data~[3]. We also discuss the additional degree of freedom provided by adding an infrared field [4] and comparing the PADs of the sidebands obtained by time-dependent calculations and the strong-field approximation. [1] K. C. Prince et al., Nature Photon.~{\bf 10} (2016) 176. [2] N. Douguet et al., Eur.~Phys.~J.~D~{\bf 71} (2017), in press. [3] G. Sansone et al., private communication (2017). [4] N. Douguet, A. N. Grum-Grzhimailo, and K. Bartschat, Phys.~Rev.~A~{\bf 95} (2017) 013407. [Preview Abstract] |
Wednesday, June 7, 2017 12:00PM - 12:30PM |
H7.00007: Time and momentum-resolved phonon decay Invited Speaker: David Reis The high brightness of x-ray free-electron lasers provides us a unique opportunity to measure lattice dynamics directly in the time domain and out of equilibrium. As a first step in this direction we demonstrate how ultrafast optical excitation creates temporal coherences in the mean-square phonon displacements spanning the Brillouin zone by a second-order squeezing process. This leads to broad-bandwidth high-resolution measurements of the phonon dispersion without the need for high-resolution monochromators or analyzers. We will also show how anharmonic phonon decay can be viewed as a parametric squeezing process, and present first momentum-resolved measurements of the downconversion of a coherent optical phonon into pairs of high-wavevector acoustic modes, information that cannot be obtained by spectroscopic measurements in the frequency domain. [Preview Abstract] |
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