Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session U01: Atoms, Molecules and Clusters in Strong FieldsLive
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Chair: Uwe Thumm, Kansas State University |
Thursday, June 3, 2021 2:00PM - 2:12PM Live |
U01.00001: Tunneling, Stark-Shifts, and Nearest Neighbor Effects for Full Valence Shell, Ultrahigh Intensity Laser Ionization of Carbon Monoxide Barry C Walker, Cara McDonald, Jimmy Williams, Evan Jones, Liam Kelley, Rachael McIntyre, Bailey Singer, Cara Nel The strong and ultrastrong field-molecule interaction is a complex, many-body interaction involving multiple ionization processes. We present experimental ion yields and molecular fragment energies for the ionization of carbon monoxide (12C 16O and 13C 18O) in a laser field with intensities spanning from 1014 W/cm2 to 1017 W/cm2. The work addresses specifically the formation of high charge states corresponding to the complete removal of the valence electrons from carbon and oxygen. Detailed saturation intensities for each ion channel are reported. Our theory model of the ionization includes tunneling, bound state Stark-shifts, nearest neighbor ion Coulomb fields, and the molecular dissociation dynamics. The ion energy spectra (with average energies of 20eV for example with O6+) show no dependence on the field intensity and are attributed to dissociative molecular ionization. The ionization of the neutral molecule to form the parent ion is shown to have a minimal effect on the formation of the highest charge states beyond initiating enhanced field ionization from the nearest neighbor ions. Atomic-like ionization is observed only when the ionization of the tightly bound ion states is unaffected by nearest neighbor fields. |
Thursday, June 3, 2021 2:12PM - 2:24PM Live |
U01.00002: Frustrated ionization in strongly driven triatomic molecules. A. Emmanouilidou, Matthew B Peters, G.P. Katsoulis We employ a three-dimensional semi-classical model, to demonstrate a significant enhancement of “frustrated’’ double ionization in the two-electron triatomic molecule D3+, driven by counter-rotating two-colour circular laser fields. The enhancement of the probability is due to a pathway, which does not appear in strongly driven molecules with linear fields. In this pathway, the first ionization step is “frustrated” and electronic correlation is negligible. We also employ a simple model that predicts many of the main features of the probabilities of the “frustrated’’ double ionization. |
Thursday, June 3, 2021 2:24PM - 2:36PM Live |
U01.00003: The role of spin in the strong-field ionization of the triplet ground state of oxygen Tomthin Nganba Wangjam, Huynh Van Sa Lam, Vinod Kumarappan We have demonstrated the spin-rotation coupling involvement in the strong-field ionization of cold oxygen molecules. This experiment is performed with a low power 800 nm pump pulse which excites a few rotational Raman cycles making sure that the multiple Raman excitation does not overshadow the spin coupled excitations, this process is probed by a strong 800 nm short pulse with strong-field ionization of the molecule. This coupling leads to an interesting observation of non-periodic structure in the time-domain which is otherwise, a periodic revival structure for the same class of molecule. We have modeled the ground state dynamics using Hund’s basis (b), with an assumption that polarizability only affects the alignment of the molecule, the time-dependent Schrödinger equation has been solved and this allows us to used fit the dynamics using the Orientation Resolution through Rotational Coherence Spectroscopy (ORRCS) procedure. |
Thursday, June 3, 2021 2:36PM - 2:48PM Live |
U01.00004: Adiabatic theory of strong-field ionization of molecules with nuclear motion Jens Svensmark, Toru Morishita, Oleg I Tolstikhin Jens Svensmark1, Oleg I. Tolstikhin2 and Toru Morishita1 |
Thursday, June 3, 2021 2:48PM - 3:00PM Live |
U01.00005: Clocking enhanced ionization of hydrogen molecules using molecular rotational wavepackets Yonghao Mi Laser-induced rotational wavepackets of hydrogen molecules have been experimentally observed in real-time by using two sequential 25-fs laser pulses (pump-probe scheme) and a COLTRIMs spectrometer. By measuring the time-dependent yield of the above-threshold dissociation and the enhanced ionization of the molecule, we observed a few-femtosecond time delay in between the two dissociation pathways for both H2 and D2. The delay was understood and interpreted by a classical model that considers enhanced ionization and thus additional interaction within the laser pulse. We demonstrate the molecule rotational clock in hydrogen molecule is a straightforward method for timing ultrafast molecular dissociation dynamics. |
Thursday, June 3, 2021 3:00PM - 3:12PM Live |
U01.00006: High-resolution FFT spectroscopy of strong-field dissociative photoionization of molecular oxygen by 800 nm pulses Vinod Kumarappan, Tomthin Nganba Wangjam, Huynh Van Sa V Lam We investigate the wavepacket that remains bound in excited cationic states of oxygen after interaction iwth an intense 45-fs, 800-nm pulse. A much weaker probe pulse is used to dissociate these still-bound molecules. The momentum distribution of O+ is measured as a function of pump-probe delay and then Fourier transformed to obtain rotational-state-resolved quantum beat spectra. The sub-cm-1 resolution of the Fourier transform allows unambiguous identification of the electronic, vibrational and rotational states populated by the pump and then disscociated by the probe. Although tunnel ionization is expected to populate the lower-lying a4∏g state more effectively than the b4∑−g state, the Fourier spectrum shows no signature of a wavepacket in the former. All the identifiable lines are due to rotational states in the higher-lying b manifold. The experiment confirms the role resonant coupling between the two states by the 800 nm pulses [1] and reveals the importance of rovibrational excitation and predissociation in determining the momentum spectrum of the O+ fragments. |
Thursday, June 3, 2021 3:12PM - 3:24PM Live |
U01.00007: Strong Field Ionization of Water II: Electronic and Nuclear Dynamics En Route to Double Ionization Chuan Cheng, Zachary Streeter, Andrew J Howard, Michael Spanner, Robert R Lucchese, C W McCurdy, Thomas Weinacht, Philip H Bucksbaum, Ruaridh Forbes The Strong Field Ionization (SFI) is an important tool to study molecular dynamics. For a small system as I$_2$, it could be used to map the Wigner distribution of the wave function [1] assuming the pulse is short enough. Usually 10fs is short enough to probe most molecular dynamics as if the nuclear motion is "frozen" in such a short period [2] so the transitions are "vertical transition". Yet our recent experiments on D$_2$O seems to indicate that the story is not that simple. Here we apply the strong field ionization to doubly ionize the deuterated water (D$_2$O) molecule. Using coincidence Velocity Map Imaging (VMI) machine, we get both electrons and ions simultaneously which is recorded using Timepix3 camera [3]. Comparing our momentum resolved D$^+$/D$^+$/O channel and the theory prediction outlined in [4] suggests the 10fs pulse is not a vertical transition. We try to explain such discrepancy between experiment and theory from some known strong field effects like the R-dependent ionization [5]. |
Thursday, June 3, 2021 3:24PM - 3:36PM Live |
U01.00008: Strong-field triple ionization of atoms with the p3 and ns2p1 valence shells studied with a reduced geometry model Jakub S Prauzner-Bechcicki, Dmitry Efimov, Michal Mandrysz, Jakub Zakrzewski Our basic understanding of multiphoton processes in atoms exposed to strong laser field is based on the single active electron picture. Effects like a multiple non-sequential ionization are beyond description in this approach. In such cases, classical or semi-classical descriptions are used typically [1, 2]. Yet, it is possible to construct a model with a reduced geometry that enables a quantomechanical study of triple ionization [3]. In such a case, a special attention must be paid to the electronic configuration of the target atom. We have studied the influence of the symmetry of initial wave function onto ionization yields in a 3-electron systems exposing the difference in hierarchy of processes contributing to triple ionization when comparing atoms with the p3 and ns2np1 valence shells [3,4]. Additionally, the effect of the third electron onto double ionization in those systems is investigated [5, 6]. |
Thursday, June 3, 2021 3:36PM - 3:48PM Live |
U01.00009: Branching Ratios from Single Ionization of CS+ by Intense Laser Pulses Tiana A Townsend, Eric Wells, Bethany C Jochim, Travis Severt, Kelsie Betsch, M. Zohrabi, Benjamin Berry, Adam Summers, Kevin D Carnes, Itzik Ben-Itzhak Employing a coincidence three-dimensional momentum imaging technique, we investigate the ultrafast, intense laser-induced ionization of CS+. The analysis presented here focuses on the intensity-dependent branching ratio from 3×1014 to 3×1016 W/cm2. The charge-symmetric C+ + S+ channel is dominant at all measured intensities, followed by CS2+ and then C + S2+, while C2+ + S is not observed. The branching ratio measurement is assisted by in situ determination of the detection efficiency of all the product channels. |
Thursday, June 3, 2021 3:48PM - 4:00PM Live |
U01.00010: Probing femtosecond dynamics of laser-heated noble-gas cluster explosions with NIR-wavelength-scanning technique Vyacheslav Leshchenko, Bryan Smith, Abraham Camacho Garibay, Li Fang, Pierre Agostini, Louis F DiMauro Clusters, having near solid density but nanometer scale and being in the transition matter state between molecules and solids, are important objects for studies of fundamental phenomena and applications. Despite a few decades of cluster research, many aspects of laser-cluster interactions remain ambiguous, especially at early stages after ionization. In order to shed light on these processes, we experimentally study femtosecond dynamics of expanding nano-plasmas from laser-ionized noble-gas clusters. Our experimental approach is based on detecting ion kinetic energy distribution in a pump-probe setup with a wavelength-scanning technique. When the frequency of collective motion of quasi-free electrons in the cluster coincides with the frequency of the probe pulse, plasma resonantly absorbs radiation, which results in an enhanced yield and energy of detected ions. A series of pump-probe scans captured at a set of probe wavelengths ranging near- and mid-infrared spectral regions (1–2.5 µm) equates to mapping the time resolved cluster density and the corresponding cluster size. The result is important for optimization of laser-matter/plasma interaction models and applications, e.g. optimization of generation of energetic charged particles and x-ray radiation. |
Thursday, June 3, 2021 4:00PM - 4:12PM On Demand |
U01.00011: Investigation of the doubly excited autoionizing states in Helium-like ions Marc-André Albert, Stéphane Laulan, Samira Barmaki The recent advent of X-ray free electron lasers (XFELs) opens the possibility to trigger the formation of doubly excited autoionizing states (DEAS) in atoms and to investigate their role in the ionization process. Accurate theoretical knowledge of where these states can be located in the energy spectrum of the targeted system and their precise lifetime decay will be a support to the future experiments on the laser-atom processes involving the DEAS. In this work, we theoretically investigate the DEAS in the Helium-like O6+ and F7+ ions by using a B-spline based spectral approach [1,2] combined with the complex rotation method [3]. We show how our method has successfully detected new high lying DEAS in the O6+ion [4] and the F7+ ion. The method generates precise values of the energy positions and lifetime decays of the DEAS. It also allows the identification of the states that share similar angular correlation pattern. The theoretical results generated in this work will be of great interest to the future experiments on the O6+ and F7+ with XFELs. |
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