Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session J03: FOCUS: Imaging and novel spectroscopy techniques |
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Chair: An-Thu Le, Missouri University of Science and Technology Room: Wisconsin Center 101CD |
Wednesday, May 29, 2019 10:30AM - 11:00AM |
J03.00001: Time-resolving electron dynamics in molecules using strong laser fields: coherent probes of charge migration Invited Speaker: Francois Mauger When forced out of equilibrium, electrons in matter can respond exceedingly fast, leading to migration of charges on time-scales approaching the attosecond [1] and before the dynamic is impacted by the weaker coupling to a system ``bath'' with many degrees of freedom. This potentially complex quantum evolution can expose correlations between electrons and holes that are otherwise hidden in the static properties of the system. Probing the electronic structure and dynamics of molecules on the attosecond time scale is, however, a formidable challenge that requires state-of-the-art experimental setups and new theoretical tools and models. In this contribution, I will discuss time-resolving charge migration using strong laser fields and present a picture of charge migration that combines strong-field dynamics [2] with the quantum-chemistry-derived electronic structure of complex molecules [3]. Using a related set of molecules as examples, I will compare experimental measurements with the results of theoretical models and associated numerical simulations to unveil the time-dependent electronic structure [4]. [1] J. Phys. Chem. Lett. 8, 3991 (2017). [2] Phys. Rev. A 93, 043815 (2016); Phys. Rev. A 97, 043407 (2018). [3] J. Chem. Phys. 145, 094105 (2016). [4] Phys. Rev. A 98, 043425 (2018); Appl. Sci. 8, 1129 (2018). [Preview Abstract] |
Wednesday, May 29, 2019 11:00AM - 11:12AM |
J03.00002: Combining Structural and Spectroscopic Probes of Molecular Dynamics Yusong Liu, Spencer Horton, Jie Yang, Thomas Wolf, Pedro Nunes, Ruaridh Forbes, Varun Makhija, Paul Hockett, Rune Lausten, Albert Stolow, Philipp Marquetand, Tamas Rozgonyi, Xijie Wang, Thomas Weinacht We combine ultrafast electron diffraction (UED) measurements with time resolved photoelectron spectroscopy (TPRES) measurements of excited state molecular dynamics. Both measurements are compared with trajectory surface hopping calculations of the dynamics, which can produce the measurement observables in both cases. The measurements highlight the non-local dynamics captured by different groups of trajectories in the calculations.~ This is the first time that both structural and spectroscopic measurements are combined with a theory capable of calculating the measurement observables in both cases, and the combination yields an unprecedented view of the multidimensional coupled electron nuclear dynamics involved in the molecular relaxation. [Preview Abstract] |
Wednesday, May 29, 2019 11:12AM - 11:24AM |
J03.00003: The role of transient resonances for ultra-fast imaging Christoph Bostedt, Phay Ho, Andre Al Haddad, Max Bucher, Gilles Doumy, Stephen Southworth, Christopher Knight, Linda Young, Tais Gorkhover, Peter Walter, Benedikt Daurer, Janos Hajdu, Filipe Maia Ultrafast imaging with intense short pulses from X-ray free-electron lasers is a promising route to investigate the structure and dynamics of nanoscale systems. The ultrafast imaging process is subject to the sample electronic structure, opening new opportunities to investigate dynamics on the shortest time scales. We have developed a computational approach for describing ultrafast imaging experiments and compare it to benchmark data from succrose clsuters. We find that transient phenomena driven by non-linear x-ray interaction are decisive for ultrafast imaging applications and that transient resonances can be exploited to increase the scattering response and elemental contrast. Our study illuminates the complex interplay of the imaging process with the rapidly changing transient electronic structures in XFEL experiments and shows how computational models allow optimization of the parameters for ultrafast imaging experiments. [Preview Abstract] |
Wednesday, May 29, 2019 11:24AM - 11:54AM |
J03.00004: Native frames: Separating sequential from concerted three-body fragmentation by coincidence three-dimensional momentum imaging Invited Speaker: Itzik Ben-Itzhak Advances in imaging techniques have led to better understanding of molecular fragmentation induced by photons or collisions. Experimental distinction between concerted and sequential (sometimes called “stepwise”) fragmentation mechanisms in polyatomic molecules is a long-standing goal. Key to its achievement is the coincidence detection of all fragments. \break \vskip 0.01in Using laser driven fragmentation of OCS and employing coincidence three-dimensional momentum imaging, we have recently demonstrated a novel method that enables the clear separation of sequential and concerted breakup [Phys. Rev. Lett. {\bf 120}, 103001 (2018)]. The separation is accomplished by analyzing the three-body fragmentation in the native frame associated with each step and using the rotation of the intermediate molecular fragment, before it undergoes unimolecular dissociation, as the signature of the sequential process. \break \vskip 0.01in Although we have demonstrated the method’s benefits using OCS fragmentation by intense laser pulses, it is not limited to a specific molecule or to the interaction causing fragmentation. The method can in fact be applied to a wide variety of systems – and they need not be charged – that undergo three-body breakup. A sample of our recent molecular-fragmentation studies employing the “Native frames” analysis will be presented. [Preview Abstract] |
Wednesday, May 29, 2019 11:54AM - 12:06PM |
J03.00005: Plasmonic-field reconstruction with atomic spatiotemporal resolution. Erfan Saydanzad, Jianxiong Li, Uwe Thumm We propose schemes for reconstructing induced plasmonic fields at the surface of isolated nanoparticles from infrared-streaked extreme-ultraviolet photoemission spectra with sub-femtosecond temporal and sub-nanometer spatial resolution. We image the plasmonic fields using both quantum-mechanical [1] and a classical [2] models that are valid for different ranges of laser and XUV-pulse parameters. The applicability of each method will be discussed for different pulse characteristics. Our numerical applications to Au nanospheres demonstrate highly accurate plasmonic field retrievals. [1] J. Li, E. Saydanzad, and U. Thumm, Phys. Rev. Lett. 120, 223903 (2018). [2] E. Saydanzad, J. Li, and U. Thumm, Phys. Rev. A 98, 063422 (2018). [Preview Abstract] |
Wednesday, May 29, 2019 12:06PM - 12:18PM |
J03.00006: Laser control of the electron wave function in transmission electron microscopy O. Schwartz, J. J. Axelrod, S. L. Campbell, C. Turnbaugh, R. M. Glaeser, H. M\"uller Laser-based manipulation of atoms and molecules is key to modern metrology and enables quantum simulation, sensing, and information processing. The emergent field of laser control of free electrons has applications ranging from compact accelerators to new electron-based imaging methods. So far, research in this field has focused on temporal modulation of the electron wave functions, which enabled ultrafast transmission electron microscopy (TEM) and diffraction. However, coherent spatial shaping of the electron wave function is needed to efficiently probe radiation-sensitive systems, such as biological macromolecules. I will present recent results on spatial manipulation of the electron wave front in a TEM via electron retardation in a high-intensity continuous-wave laser beam. We have realized an electron interferometer using a standing light wave as a beam-splitter and phase retarder, and captured TEM images of the light wave. We then used laser-induced electron retardation to demonstrate Zernike phase contrast in TEM, and achieved a substantial increase of image contrast. Laser-based Zernike phase contrast will advance TEM studies of protein structure, cell organization, and complex materials. [Preview Abstract] |
Wednesday, May 29, 2019 12:18PM - 12:30PM |
J03.00007: First demonstration of high-precision Ramsey-comb spectroscopy in the VUV spectral range Laura Dreissen, Charlaine Roth, Elmer Grundeman, Maxime Favier, Julian Krauth, Kjeld Eikema High-precision spectroscopy of simple atomic systems, such as atomic hydrogen, enables stringent tests of bound-state quantum electrodynamics (QED). Frequency measurements on e.g. singly-ionized helium could provide more stringent tests, enable a new determination of the Rydberg constant or the alpha particle charge radius. For this purpose, we developed precision frequency metrology at vacuum-UV (VUV) and shorter wavelengths by combining Ramsey-Comb Spectroscopy (RCS) with High-Harmonic Generation (HHG) for the first time. In RCS, the transition frequency is determined from the phase of Ramsey fringes recorded with pairs of amplified frequency-comb pulses at different multiples of the comb repetition time. A combination with HHG could introduce detrimental phase shifts from plasma formation. We show this is circumvented by introducing a minimum pulse delay of 16ns, and demonstrate a measurement of the 5p$\rightarrow$8s transition xenon at 110nm (7$^{th}$ harmonic) with a preliminary relative accuracy of $<$5*10$^{-10}$ ($\approx$1MHz, more than a 1000-fold improvement on the transition). The accuracy is mainly limited by the transit time of xenon through the refocused VUV beam and shows that this method is very promising for precision metrology of the 1S-2S transition in He$^+$. [Preview Abstract] |
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