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 V05: Atoms, Molecules, and Clusters in Strong Fields |
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Chair: Julien Bertrand, Université Laval Room: Grand E |
Friday, June 1, 2018 10:30AM - 10:42AM |
V05.00001: Frustrated tunnel ionization in the few-cycle regime R.D. Glover, D. Chetty, A.J. Palmer, B.A. deHarak, J.L. Holdsworth, M.A. Dakka, A.N. Luiten, P.S. Light, I.V. Litvinyuk, R.T. Sang Frustrated Tunnel Ionization (FTI) is a strong-field phenomenon where an ultrashort laser pulse excites a target atom, leaving it in a Rydberg state~[Nubbemeyer, T., et al. Phys. Rev. Lett. 101(23): 233001 (2008)]. This occurs after a tunneling ionization event when the dominant ionization channel is `frustrated' by the atomic Coulomb potential. Studying the mechanism behind FTI facilitates our understanding of atomic and molecular strong-field dynamics; e.g. FTI is observed in time-resolved ionization dynamics [Sabbar, M., et al. Nat. Phys. 13(5): 472-478 (2017)] and delayed ionization~[Larimian, S., et al. Phys. Rev. A 94(3) (2016)], and the fragmentation of molecules~[Manschwetus, B., et al. Phys. Rev. Lett. 102(11): 113002 (2009)]. Here we compare our experimental and theoretical FTI yields for few- and multi-cycle pulses. We find that for the same pulse energy more FTI is generated with few-cycle pulses. [Preview Abstract] |
Friday, June 1, 2018 10:42AM - 10:54AM |
V05.00002: Impact of atomic Rydberg state excitation on the radiation spectrum generated in short intense laser pulses Joel Venzke, Ran Reiff, Zetong Xue, Agnieszka Jaron-Becker, Andreas Becker The impact of highly excited (Rydberg) states on strong-field induced high harmonic generation and ionization has been of recent interest. Utilizing {\it ab initio} simulations of the Time Dependent Schr\"{o}dinger Equation and systematically selecting laser intensities and frequencies, the distribution across the angular momentum states is analyzed for resonant absorption of odd and even number of photons. Furthermore, signatures of the population in the excited states in the radiation spectrum generated during the pulse and after the pulse are identified. [Preview Abstract] |
Friday, June 1, 2018 10:54AM - 11:06AM |
V05.00003: Resonant Enhancement of Strong Field Inner Orbital Ionization of Molecular Iodine George Gibson, Dale Smith We present a wavelength study of the strong field single electron ionization of molecular iodine near its one-photon B-state resonance at 530 nm which shows a remarkably strong wavelength dependence. We have previously identified two ionization channels (PRA 95, 013410): ionization of the high lying molecular orbitals and ionization of the deep orbitals in $I_2$. We find a resonant enhancement of both channels, although the peak enhancement occurs at different wavelengths for the different channels. Moreover, the branching ratio of the ionization of the deep orbitals shows a dispersion-like function, with the branching ratio of the deep orbitals reaching over 98\% at 519 nm. Finally, the branching ratio of double ionization into an excited state of $I_2^{2+}$ as a function of wavelength closely matches the branching ratio of the single ionization of deep orbitals, implying that excitation of molecular ions generally comes about through inner orbital ionization. [Preview Abstract] |
Friday, June 1, 2018 11:06AM - 11:18AM |
V05.00004: Atomic single-active-electron potential and application to intense field processes Ran Reiff, Tennesse Joyce, Michelle Miller, Erez Shani, Agnieszka Jaron-Becker, Andreas Becker Simulations of interaction of multielectron atoms with intense laser fields are computationally expensive. Therefore, often the single-active electron (SAE) approximation is used. We present a method for generating SAE potentials for atoms and ions, based on density functional theory calculations. Exact potentials are fit to physically-motivated analytic forms dependent on the orbital structure. Applications to simulation of high harmonic generation will be presented. [Preview Abstract] |
Friday, June 1, 2018 11:18AM - 11:30AM |
V05.00005: Strong Field Ionization of hydrogen in bi-circular fields Philipp M. Stammer, Felipe Morales, Olga Smirnova, Mikhail Ivanov Interaction of a strong laser field with an atom or a molecule is often described in a simple three-step picture: an electron is tunnel ionized, then it is accelerated away from the core, to be finally driven back to the parent ion, by the laser field. The recollision or the rescattering with the parent ion is at the heart of strong-field phenomena, i.e. High Harmonic Generation (HHG) and Above Threshold Ionization (ATI). While a circularly polarized laser field does not allow for recollision, a bi-circular field (consisting of two co-planar, counter-rotating, circularly polarized laser fields) does. Bi-circular HHG has been studied both experimentally and theoretically, whereas research on ATI spectra in these fields has been mostly limited to analytical studies. In this work we present ATI spectra calculated via direct solution of the Time Depending Schr\"{o}dinger Equation for the Hydrogen atom, exposed to an intense bi-circular field. These calculations are computationally demanding, and will help to understand the underlying physics, and confirm the analytical predictions. The emitted photo-electrons exhibit the same three-leaf structure as the electric field, but also deflections and structure due to the interaction with the Coulomb potential will be discussed. [Preview Abstract] |
Friday, June 1, 2018 11:30AM - 11:42AM |
V05.00006: Molecular and Pulse Symmetry Effects in Bichromatic Circularly Polarized High Order Harmonic Generation . Andre Bandrauk, Kai Jun Yuan We present from quantum numerical simulations molecular and pulse symmetry effects in circularly polarized HHG,,high order harmonic generation,,with counter-rotating bichromatic circularly polarized intense laser pulses.We discuss how electron recollision trajectories[1] influence the harmonic polarizations from a time-frequency analysis of the harmonics.It is found that molecular orientation dependent ionization rates determine the harmonic polarizations especially below 2 Up energies due to Coulomb potentials.Coriolis effects in a rotating frame ,predicted as early as 1995[2],are shown to also influence HHG polarizations.Electron recollision trajectories illustrate the effects of relative molecule-pulse electric field symmetries on efficiencies and polarizations of bicircular bichromatic HHG [1]AD Bandrauk,F Mauger,KJ Yuan,J Phys B 49,23LT01(2016);[2]T Zuo,AD Bandrauk,J Nonlin Opt.Phys Mat 04,533(1995);AD Bandrauk,HZ Lu,Phys Rev A 68,043408(2003).. [Preview Abstract] |
Friday, June 1, 2018 11:42AM - 11:54AM |
V05.00007: Relativistic non-dipole effects in strong field ionisation Nida Haram, Han Xu, Atia-Tul Noor, Satya Sainadh Undurti, Igor Ivanov, Igor Litvinyuk, Robert Sang Breakdown of dipole approximation in strong field ionisation has been investigated experimentally earlier [Phys.Rev.Lett.\textbf{106},193002 (2011); Phys.Rev.Lett.\textbf{113},243001 (2014)] - Those experimental results have been interpreted using different theoretical approaches. For certain laser parameters, the peaks of transverse electron momentum distributions (TEMD)s were found to be shifted forward along the laser propagation direction due to the radiation pressure caused by the Lorentz force. However, in the long wavelength limit, at intensities as low as 10$^{\mathrm{13}}$ W/cm$^{\mathrm{2}}$, the counter-intuitive shifts opposite to the laser propagation direction were reported. \textbf{In this work}, we explore the non-dipole effects on the TEMD of noble gas atoms (Ar) at intensities greater than 5 x 10$^{\mathrm{14}}$ W/cm$^{\mathrm{2}}$. The TEMD along the laser propagation direction are recorded with a reaction microscope using few cycle (6-7 fs) near-infrared (800 nm) linearly polarized laser pulses. In agreement with the fully relativistic theoretical results based on the time-dependent Dirac equation, we report increasing counter-intuitive peak shifts with increasing laser intensities. The underlying mechanism of these counter-intuitive dynamics can be explained on the basis of interplay between the Coulomb potential and the Lorentz force. [Preview Abstract] |
Friday, June 1, 2018 11:54AM - 12:06PM |
V05.00008: Strong-field laser induced H$_{\mathrm{2}}$ roaming reactions and the formation of H$_{\mathrm{3}}^{\mathrm{+}}$ from organic molecules N. Ekanayake, M. Nairat, T. Severt, P. Feizollah, B. Jochim, B. Kaderiya, F. Ziaee, K. Borne, Kanaka Raju P., K. D. Carnes, D. Rolles, A. Rudenko, I. Ben-Itzhak, N. P. Weingartz, B. M. Farris, J. E. Jackson, B. G. Levine, M. Dantus Roaming chemical reactions are a novel chapter in our understanding of certain exotic reactions relevant to molecular physics, photochemistry, and combustion chemistry. A recent finding indicating the involvement of H$_{\mathrm{2}}$ roaming for the formation of H$_{\mathrm{3}}^{\mathrm{+}}$ under strong-field photodissociation [Ekanayake, N. \textit{et al}. \textit{Sci. Rep.} \textbf{7}, 4703 (2017)] inspired a series of experiments aimed at elucidating aspects of its mechanisms of formation. In the present study, site-specific details and femtosecond time-resolved dynamics of H$_{\mathrm{3}}^{\mathrm{+}}$ formation were obtained through a combination of strong-field laser excitation studies and \textit{ab initio} calculations on a series of alcohols. Our findings confirm the mechanisms of this intriguing chemical process involving the cleavage and formation of three chemical bonds and reveal that H$_{\mathrm{3}}^{\mathrm{+}}$ yields decrease as the alkane chain length increases. This new understanding will aid in the prediction of expected yields and formation times of H$_{\mathrm{3}}^{\mathrm{+}}$ from different organic molecules. [Preview Abstract] |
Friday, June 1, 2018 12:06PM - 12:18PM |
V05.00009: Imaging of metastable $\textrm{CO}_2$ ions dissociating in flight Reid Erdwien, Bethany Jochim, Peyman Feizollah, T. Severt, Ben Berry, B. Kaderiya, F. Ziaee, Kanaku Raju P., K.D. Carnes, D. Rolles, A. Rudenko, I. Ben-Itzhak Fragmentation of $\textrm{CO}_2$ molecular ions is a commonly studied process. We examine unimolecular dissociation in flight of metastable $\textrm{CO}_2^{2+}$ ions employing the cold target recoil ion momentum spectroscopy (COLTRIMS) technique. The metastable states responsible for dissociation in flight are populated by ultrashort laser pulses. Data analysis is conducted using a previously described method [1]. Analysis of the high statistics delayed $\textrm{CO}_2^{2+} \rightarrow \textrm{CO}^+ + \textrm{O}^+$ channel allows us to further demonstrate the power of our method, in particular the direct determination of the lifetime(s) of the decaying state(s) without the need for simulations typically required by other methods. We also extract the 3-D momentum distributions of the dissociating fragments. We compare our findings to existing results. \\ {[1]} Bethany Jochim et al., New J. Phys. \textbf{19}, 103006 (2017). [Preview Abstract] |
Friday, June 1, 2018 12:18PM - 12:30PM |
V05.00010: Stability of the rotating Lewis-Langmuir cubic atom in the Circularly Polarized Electromagnetic and the Magnetic Fields Matt Kalinski We consider a fully saturated true Lewis-Langmuir [1-2] atom when all of the eight electrons are occupying the corners of the cube. Such symmetric configuration exists for the arbitrary edge length without rotation for the resonant mathematical value of the nuclear ion charge $Z^*=(6 \sqrt{3}+3 \sqrt{6}+2)/8 = 2.4676$. When $Z>Z^*$ the existence of the atom must be forced by the rotation and when $Z < Z^*$ by the compressing rotation in the magnetic field both with the square cuboidal deformation. When the rotating electric field is added the atom further deforms to the trapezoidal hexahedron. We study the classical dynamic stability of the configuration when the stable classical configuration is resulting in the 8-electron nondispersing wave packets localized around the edges of the configuration building the quantum atom. We find the stability islands much more exotic then for our recently discovered two electron Langmuir configurations in the helium atom. Exact quantum time dependent numerical simulations of the nondispersing 24-dimensional wave packets using our new recently discovered Time Dependent Quantum Diffusion Monte Carlo Method are also provided. [1] G. N. Lewis, J. Am. Chem. Soc. {\bf 38}, 762, (1916) [2] I. Langmuir, J. Am. Chem. Soc. {\bf 41}, 868, (1919) [Preview Abstract] |
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