Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 67, Number 7
Monday–Friday, May 30–June 3 2022; Orlando, Florida
Session C10: Focus Session: Atoms and Molecules in Strong Laser FieldsFocus Live Streamed
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Chair: Eric Wells, Augustana Univ Room: Grand Ballroom D |
Tuesday, May 31, 2022 11:00AM - 11:30AM |
C10.00001: Revealing the influence of molecular chirality on tunnel-ionization dynamics Invited Speaker: Yann Mairesse Strong-field light-matter interaction enables probing atomic and molecular structures and dynamics with unprecedented resolutions. The primary event common to all strong-field spectroscopies is tunnel-ionization through the target potential barrier lowered by the laser field. The tunneling dynamics and the complex properties of the outgoing electron are difficult to isolate from its subsequent scattering onto the ionic potential. To reveal them, we have performed a joint experimental and theoretical study using a specific target: chiral molecules, whose photoionization by circularly polarized light produces forward-backward asymmetric electron distributions with respect to the light propagation direction. These asymmetric patterns provide a background-free signature of the chiral potential in the ionization process. |
Tuesday, May 31, 2022 11:30AM - 11:42AM |
C10.00002: Weak-field asymptotic theory – an efficient and accurate alternative to the time-dependent DFT for ionization calculations Imam S Wahyutama, Denawakage D Jayasinghe, Francois Mauger, Mette B Gaarde, Kenneth Lopata, Kenneth J Schafer Strong-field ionization (SFI) is a process that is sensitive to the instantaneous field strength, making SFI a promising tool for time-resolving the study of ultrafast dynamics in molecules. The common method by which one calculates ionization is by propagating a given initial state and analyzing the portion of the wave function that ventures far enough from the nuclei. This method, however, becomes very expensive as basis requirements increase (e.g. as electron energy increases). Using Gaussian basis sets remedies this problem, but the so-called leakage flux issue now becomes relevant. Here, we implement the weak-field asymptotic theory (WFAT) using orbitals obtained through density functional theory. To validate the use of WFAT for representing ionization from time-dependent simulations, we compare angle-resolved ionizations of both methods for some molecules. We also develop a many-electron extension of WFAT that is essential for analyzing the effect of neutral excited states on the ionization. |
Tuesday, May 31, 2022 11:42AM - 11:54AM |
C10.00003: A General Method of Time Correlation Retrieval for Quantum Interference in Strong-Field Ionization Nicholas Werby, Andrew S Maxwell, Ruaridh Forbes, Carla Figueira de Morisson Faria, James P Cryan, Philip H Bucksbaum In laser-induced strong-field ionization (SFI), photoelectrons escape the parent ion and oscillate on semi-classical trajectories within the laser field. These trajectories are determined primarily by the phase in the laser field at which ionization occurred and the shape of the laser field. As an electron travels along a trajectory it accumulates phase, which produces quantum interference structures when pairs of trajectories contribute to the final amplitude. When acquiring the photoelectron momentum distribution (PMD) through angle- and energy-resolved detection systems such as velocity map imaging, these quantum interferences manifest as intricate, overlapping patterns on the detector. Much study has focused on unraveling these patterns in order to understand the ultrafast electron dynamics integral to their formation. We introduce and apply a broadly applicable time correlation filtering technique which isolates interference structures formed by trajectory pairs whose ionization phases are separated by a specified time. By examining the time correlations at which structures are emphasized, we empirically corroborate predictions from a leading theoretical model of SFI. Based on the selected time correlation, interference patterns produced by specific pairs of trajectories can be isolated, allowing for in depth quantitative studies of rescattering orbits and the structure of the parent ion. As an analysis technique, this time resolution can be achieved for all angle- and energy-resolved PMDs, unlocking a powerful observable without requiring any changes in experimental schema. The generality of the filtering technique combined with its ability to disentangle complex experimental spectra will greatly augment the level of analysis that can be performed on this type of data. |
Tuesday, May 31, 2022 11:54AM - 12:06PM |
C10.00004: Quantum interference in strong-field ionization by a linearly polarized laser pulse explains non-zero tunnel exit momentum Attila Czirják, Szabolcs Hack, Szilárd Majorosi, Mihaly Benedict, Sándor Varró We theoretically and numerically investigate the liberation of an atomic electron by a linearly polarized single-cycle near-infrared laser pulse with a peak intensity corresponding to tunnel ionization. This process is of fundamental importance in attosecond physics, with open questions regarding e.g. the tunnel exit momentum. |
Tuesday, May 31, 2022 12:06PM - 12:36PM |
C10.00005: Multi-body fragmentation dynamics explored using coincidence momentum imaging with native frames analysis Invited Speaker: Travis Severt As both detector and light source technologies progress, experimental studies of the multi-body fragmentation of polyatomic molecules using coincidence momentum imaging become more feasible. Our goal is to gain detailed insight into both concerted and sequential (i.e. step-wise) molecular dynamics, which we accomplish by using native frames analysis [1]. |
Tuesday, May 31, 2022 12:36PM - 12:48PM |
C10.00006: Dissociative and non-dissociative ionization of CS+ by intense ultrashort laser pulses Tiana A Townsend, Eric Wells, Travis Severt, Bethany C Jochim, M. Zohrabi, Benjamin Berry, Adam M Summers, Kevin D Carnes, Itzik Ben-Itzhak We investigate the dissociative and non-dissociative ionization of a CS+ molecular-ion beam exposed to intense ultrafast laser pulses (780-nm, 25-fs, over the range 1012 – 1015 W/cm2 laser pulses at 10 kHz) by employing a coincidence three-dimensional momentum imaging technique. As expected, the C+ + S+ channel, which correlates with the lowest electronic states of CS2+, dominates over the entire intensity range studied. The measured kinetic energy release indicates that the ground and first excited states of CS2+ are the main contributors to this channel. A fraction (about 10%) of all CS2+ produced in these metastable states live long enough to reach the detector intact. We also observe the less likely (a few %) charge-asymmetric channel, C + S2+, while C2+ + S is not observed. The kinetic energy release in C + S2+ breakup is much smaller than that in the C+ + S+ fragmentation. Finally, both two-body breakup channels are found to be tightly aligned along the laser polarization. |
Tuesday, May 31, 2022 12:48PM - 1:00PM |
C10.00007: Transient Nonadiabatic Charge Redistribution in Molecules and its Effects on Nuclear Frame Dmitri A Romanov, Robert J Levis Transient nonadiabatic charge redistribution (TNCR) in a molecule or molecular ion is caused by the strong oscillating electric field of a linearly polarized femtosecond laser pulse and can be maintained throughout a major part of the pulse duration. It directly affects the motion of light components of the nuclear frame (protons) during the pulse and it is imprinted in the evolution of nuclear degrees of freedom after the pulse, most notably, in the impulsive alignment in the molecular ensemble. Prolong charge localization and sequential ionization in polyatomic molecules affects the ensuing fragmentation pattern and charge distribution among the fragments. Our model calculations of the relative yield of ionized fragments and the kinetic energy distributions of the released protons agree quantitatively with the experimental data.The TNCR-mediated interaction of the laser field with molecular rotational degree of freedom results in a characteristic composition of the rotational wavepacket that is formed by this impulseve torque and that determines the subsequent molecular alignment dynamics.TNCR and its consequences are critically influenced by many-body effects. We investigate the interplay of the charge localization and inter-electronic repulsion and the resulting modifications of the angular dependence patterns in the cumulative impulsive torque. |
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