Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session P05: Time-Resolved Electron Dynamics and Attosecond SpectroscopyLive
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Chair: Agnes Vibok, University of Debrecen Room: D139-140 |
Thursday, June 4, 2020 2:00PM - 2:12PM Live |
P05.00001: Does streaking measure time delays? Ulf Saalmann, Jan M Rost It is rigorously shown under which condition the delay from a streaking spectrogram provides the (Wigner-Smith) time delay. As this is based exclusively on energy absorption, i.\,e.\ the interplay of the binding potential and the streaking laser, it follows immediately that the long-range Coulomb potential is not standing out as the introduction of the so-called ``Coulomb-laser-coupling time'' suggests. A suitable way of defining meaningful (finite) time delays in the case of (long-range) Coulomb potentials is proposed. [Preview Abstract] |
Thursday, June 4, 2020 2:12PM - 2:24PM Live |
P05.00002: Time Delays from One-Photon Transitions in the Continuum Luca Argenti, Jaco Fuchs, Nicolas Douguet, Stefan Donsa, Fernando Mart{\'i}n, Joachim Burgd{\"o}rfer, Laura Cattaneo, Ursula Keller Photoemission time delays reveal information about the potential landscape an electron probes upon ionization. Here, we quantify the dependence of the time delay on the angular momentum of the electrons liberated by ionization of the helium atom, analyzing the energy and angularly-resolved electron distribution within a two-color attosecond pump-probe scheme. These measurements allow us to disentangle the relative phase of all quantum pathways contributing to the photoelectron signal. In particular, we retrieve the dependence on the angular momentum of the Bremsstrahlung delay, which is an essential contribution to the ionization delay observed in all attosecond pump-probe measurements. We observe a continuum-continuum transition delay between outgoing s- and d-electrons as large as 12 as close to the ionization threshold. Both single-active-electron and full \emph{ab initio} simulations confirm this observation for helium and hydrogen, suggesting that these delays are universal. [Preview Abstract] |
Thursday, June 4, 2020 2:24PM - 2:36PM Live |
P05.00003: Control of parent-ion coherence in helium ionization Saad Mehmood, Eva Lindroth, Luca Argenti Attosecond extreme ultraviolet (XUV) pulses trigger the release of a photoelectron from an atom or molecule in a coherent ionization process. As soon as the electron is emitted, however, part of the coherence in the residual parent-ion is lost, and so is the chance of guiding any subsequent transformations of the target in a reproducible way. To influence the parent-ion coherence, the system can be perturbed with additional light pulses before the ionization process is over. Here we perform XUV-pump IR-probe ionization of Helium to create a controllable coherence of the ions in the $2s$ and $2p$ states of the He$^+$ ion. Within the electrostatic approximation, these states are degenerate, and hence their coherent superposition gives rise to a parent-ion with a permanent dipole moment whose polarization beats on a time scale of few femtosecond due to delay between ionizing pulses. The dipole moment fluctuates even in absence of external fields, due to spin-orbit interactions on a picosecond timescale. The determination of the amplitude and phase of such oscillation allows to reconstruct the net parent-ion dipole moment at the time of its inception. [Preview Abstract] |
Thursday, June 4, 2020 2:36PM - 2:48PM Live |
P05.00004: Light-induced Fano structures and tunable transparency in the Argon continuum Nathan Harkema, Coleman Cariker, Sergio Yanez-Pagans, Luca Argenti, Arvinder Sandhu Several studies in Helium [1,2] have shown the existence of Lorentzian-like light-induced structures which appear as a result of two-photon (XUV + IR) transitions to the bound excited states. Here we investigate light-induced structures that appear in the Argon continuum as a result of two-photon transitions to autoionizing $3s^{-1}3d$ and $3s^{-1}5s$ states. These structures are Fano-like which implies an interference between bound and continuum pathways for the two-photon transitions. Additionally, the structures include windows of induced transparency which can be tuned in energy by adjusting the wavelength of the IR pulse. This control of absorption and transparency can be applied to XUV pulse shaping and ultrafast signal processing. We compare our experimental results with ab initio calculations to quantify the coupling parameters that determine the details of the absorption lineshapes and light-induced structures. [1] S. Chen et al., Phys. Rev. A 86, 063408 (2012). [2] M. Chini et al., Sci Rep 3, 1105 (2013) [Preview Abstract] |
Thursday, June 4, 2020 2:48PM - 3:00PM Live |
P05.00005: Autler-Townes splitting and light induced structures in the absorption profile of an autoionizing resonance Coleman Cariker, Eva Lindroth, Luca Argenti The effects of Fano interference and Autler-Townes splitting are well documented in absorption spectroscopy experiments. Recently, ultrafast pump-probe spectroscopy has demonstrated further control of these features by manipulation of the parameters of the pulse sequence. We report \emph{ab initio} calculations, in quantitative agreement with experimental measurements, demonstrating a combination of the two effects. By dressing a Fano resonance with a moderately strong probe pulse, light induced structures appear in the absorption profile, which are observed to transition into an Autler-Townes doublet feature as the probe frequency crosses the position of the dark resonance. We supplement these results with essential state model calculations that give insight into the role the various bright and dark resonances play in the driven evolution of the system and the resultant spectral features. [Preview Abstract] |
Thursday, June 4, 2020 3:00PM - 3:12PM Live |
P05.00006: Photo angular distributions of few photon ionization of atomic targets in superpositions Joel Venzke, Agnieszka Jaron-Becker, Andreas Becker Few photon ionization of atomic targets with EUV and VUV pulses has been of recent theoretical and experimental interest. This presentation will discuss photo angular distributions obtained via numerical solutions of the Time Dependent Schrodinger equation for atoms prepared in superposition of states. The impacts of pulse length and intensity on the photo angular distributions will be discussed including a generalization of the asymmetry parameters that readily distinguishes the two dominant pathways to ionization. [Preview Abstract] |
Thursday, June 4, 2020 3:12PM - 3:24PM Live |
P05.00007: Attosecond Electron Correlation and Molecular Resonance in \textit{K}-shell Photoexcitation of Nitric Oxide Taran Driver, Elio G. Champenois, James P. Cryan, Siqi Li, Agostino Marinelli, Philipp Rosenberger, Matthias F. Kling, Lisa Ortmann, Alexandra Landsman Angular streaking is employed to resolve the attosecond electronic motion of nitric oxide (NO) irradiated with intense, sub-femtosecond, soft X-ray pulses from a free-electron laser.\footnote{Duris, Li \textit{et al.}, Nat. Phot. \textbf{14}, 30 (2020)} We scan the incident photon energy through the O \textit{K}-edge and measure the dynamics of the resultant photoemission. Below the edge we drive the O $1s \rightarrow 2p\pi ^\ast$ core excitation and time-resolve the subsequent electron correlation-driven Auger decay. Above the \textit{K}-edge we measure the photon energy-dependent dynamics determining the precise release time of the O \textit{K}-shell electron into the continuum. We observe the attosecond time-delay associated with the O $1s \rightarrow 2p\sigma ^\ast$ shape resonance previously identified in cross-section measurements. [Preview Abstract] |
Thursday, June 4, 2020 3:24PM - 3:36PM Live |
P05.00008: Tailoring attosecond pulses for coherent control of electron dynamics. Guillaume Laurent, Brady Unzicker, Spenser Burrows, Morgan Tatum, John Vaughan, Trevor Hart, Davis Arthur, Patrick Stringer The recent advent of attosecond pulses of light offers new opportunities for controlling quantum dynamics in matter down to the natural timescale of electron motion. So far, attosecond control of electron dynamics has been mostly achieved with pump/probe schemes where an attosecond pump pulse triggers a given electronic process and a phase-locked femtosecond probe field is used to steer its dynamics. The dynamical system under scrutiny is thus controlled by varying the time delay between the two pulses. In this work, we show that electron dynamics can also be controlled by shaping the temporal profile of the attosecond pulse. We present details on our experimental procedure to control the photoelectron emission from atoms along the polarization direction of the ionizing field. [Preview Abstract] |
Thursday, June 4, 2020 3:36PM - 3:48PM On Demand |
P05.00009: Shortening isolated attosecond pulses from high-order harmonic generation by controlling a trajectory parameter Dian Peng, Jean Marcel Ngoko Djiokap Isolated attosecond pulses (IAPs) can be generated by spectrally filtering a high-order harmonic generation (HHG) spectrum produced by a short laser pulse. Current methods for generating shorter IAPs focus on increasing HHG cutoff energies or reducing HHG attochirp. Here, we demonstrate theoretically that the control of a trajectory parameter associated with the classical cutoff trajectory of HHG can be used to effectively reduce the HHG spectral chirp and produce IAPs of shorter duration. Based on analytic and numerical calculations of HHG spectra from an H atom produced by linearly polarized short laser pulses, we show that adjusting the laser waveform by superposing multiple (two or more) driving pulses can control this trajectory parameter and hence shorten IAP duration. [Preview Abstract] |
Thursday, June 4, 2020 3:48PM - 4:00PM On Demand |
P05.00010: Ab initio study of the quantum electronic coherences emerging from molecular attosecond ionization Marco Ruberti Here we present a new ab initio method for many-electron dynamics in polyatomic molecules, time-dependent B-spline Restricted Correlation Space-Algebraic Diagrammatic Construction (RCS-ADC)[M. Ruberti, Phys.Chem.Chem.Phys.21,17584(2019)]. RCS-ADC describes molecular ionization from first principles by combining the accurate description of electron correlation of quantum chemistry with the full account of the photoelectron continuum dynamics. We study the correlated many-electron dynamics upon attosecond ionization of pyrazine, providing a complete characterisation of the ionised state. We calculate the density matrix of the bipartite ion-photoelectron system, the ionic reduced density matrix (R-IDM), including description of correlated shakeup states, and the von Neumann entropy of the prepared entangled state. We study the ion-photoelectron interaction and unravel the mechanisms of onset and loss of quantum electronic coherences. Simulating the X-ray attosecond transient absorption measurement, by solving the von Neumann equations for a characterized R-IDM interacting with the X-ray probe field, allows us to unveil the mapping of the measurement results onto the non-zero R-IDM matrix elements. This study paves the way to the control of charged-directed photo-chemical reactivity. [Preview Abstract] |
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