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 D03: Time-resolved electron dynamics and attosecond spectroscopy |
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Chair: Boris Bergues, Max-Planck-Gesellschaft Room: Wisconsin Center 101CD |
Tuesday, May 28, 2019 2:00PM - 2:12PM |
D03.00001: A new method for spectral phase retrieval of broadband single attosecond pulses utilizing the autocorrelation of photoelectron streaking spectra Su-Ju Wang, Xi Zhao, Weiwei Yu, Hui Wei, C. D. Lin Recent progress in high-order harmonic generation with few-cycle mid-infrared lasers has pushed light pulses into the water-window region and beyond. These pulses have the bandwidth to support single attosecond pulses down to a few tens of attoseconds. An accurate characterization of such attosecond pulses is required for time-resolved probing of inner-shell electron dynamics. However, the presently available techniques for attosecond pulse measurements are not applicable to such short pulses. Here, we report a phase-retrieval method using the standard photoelectron streaking technique in the presence of an IR pulse assuming only the strong-field approximation. The new iterative algorithm allows accurate reconstruction of the spectral phase of light pulses ranging from extreme-ultraviolet to soft x-rays. Built on that, we propose further to calculate the autocorrelation (AC) of the streaking traces and use it to extract the spectral phase. The new method is found to be more accurate and more efficient especially for broadband water-window attosecond pulses. [Preview Abstract] |
Tuesday, May 28, 2019 2:12PM - 2:24PM |
D03.00002: A RABBITT attoclock for the direct measurement of photoionization time delays Luca Argenti, Nicolas Douguet, Stefan Donsa, Iva Brezinova, Joachim Burgdörfer We propose the ``RABBITT attoclock'', an XUV-pump IR-probe photoionization scheme that employs isolated pairs of counter-rotating consecutive harmonics, such as those produced with bi-circular fields [1-2], in conjunction with angularly resolved detectors. This method differs from Rainbow RABBITT [3] in two major respects: i) it gives direct access to rapidly varying photoemission delays, thus eliminating the interference from the continuum-continuum probe stage, and ii) it does not require any time-delay scan. The scheme is based on the interference between one-photon and two-photon ionization pathways whose phase difference is imprinted in the photoelectron anisotropy. We illustrate the method with \emph{ab initio} simulations [4,5] of the resonant ionization of the helium atom, showing that the angular photoelectron distribution exactly reproduces the rapid excursion of the scattering phase shift near the $(2s2p)^1$P$^{\rm o}$ resonance. [1] O. Kfir~{\it et al.}, Nat. Photonics {\bf 9}, 99 (2015). [2] P.-C. Huang~{\it et al.}, Nat. Photonics {\bf 12}, 349 (2018). [3] V. Gruson~{\it et al.}, Science {\bf 354}, 734 (2016). [4] L. Argenti~{\it et al.} Phys. Rev. A {\bf 87}, 053405 (2013). [5] S. Donsa~{\it et al.} arXiv:1811.09110 [physics.atom-ph]. [Preview Abstract] |
Tuesday, May 28, 2019 2:24PM - 2:36PM |
D03.00003: Ab initio numerical methods for attosecond molecular spectroscopy Nicolas Douguet, HEMAN GHARIBNEJAD, Barry Schneider, Luca Argenti We present our recent advances towards the development of two original numerical methods to describe the interaction between ultra-short laser pulses and correlated molecular systems. The first method, CK-LOPT [1], uses the Complex Kohn (CK) variational approach to compute multi-photon amplitudes at the lowest-order level of perturbation theory (LOPT). It can describe molecular photoionization time delay and transient absorption spectra in relatively weak fields, when only few-photon exchanges are involved. The second method, FEDVR-TDSE, uses an hybrid Gaussian and FEDVR basis set to solve the time-dependent Schr\"{o}dinger equation (TDSE), within the same close-coupling framework employed in the CK approach, and can be applied to nonpertubative regimes as well. [1] N. Douguet, B. I. Schneider, and L. Argenti, Phys. Rev. A {\bf 98} 023403 (2018), [Preview Abstract] |
Tuesday, May 28, 2019 2:36PM - 2:48PM |
D03.00004: Wave front controlled attosecond few-slit interferometry. Wei Cao, Zhen Yang, Huiyao Xu, Kang Mi A novel “wave front” controlled all-optical interferometer with high temporal resolution is presented. An intense few-cycle laser pulse drives high order harmonics and launches a few equally separated attosecond bursts, which is equivalent to a few-slit time domain interferometer and gives rise to odd number of harmonics in frequency domain. When a weak signal pulse was synchronized with the driver, it perturbs the electron trajectories for harmonic generation and alters the accumulated phase on individual attosecond pulse. This effectively builds up a tilt in the wave front of the few attosecond slits in time domain, leading to a shift in the harmonic photon energy. A simple expression for the delay dependent energy shift is derived, from which the waveform of the perturbing field becomes directly accessible, offering an efficient optical oscilloscope for characterizing petahertz electromagnetic field. In addition, the separation of adjacent time domain attosecond slits can be retrieved with a temporal resolution of 60 attosecond, providing a sensitive probe to grasp the structural information of the complex driving targets. [Preview Abstract] |
Tuesday, May 28, 2019 2:48PM - 3:00PM |
D03.00005: Temporal Observation of Interchannel Coupling in Molecular Photoionization Andrei Kamalov, Philip H. Bucksbaum, Daniel J. Haxton, James P. Cryan Molecular photoionization delays are measured for the X $^{2}\Pi_{g}$, A $^{2}\Pi_{u}$, and B $^{2}\Sigma^{+}_{u}$ cationic states of CO$_2$ using the Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT) technique. We compare these measured values with quantum mechanical calculation of the photoionization scattering phase. Our results show that interchannel continuum coupling is necessary to explain the observed result. Moreover, this interchannel continuum coupling is particularly important in the vicinity of a molecular shape resonance and near autoionizing molecular Rydberg states. This approach is a first step towards time-resolving electron correlation in molecular photoionization. [Preview Abstract] |
Tuesday, May 28, 2019 3:00PM - 3:12PM |
D03.00006: Imaging of Attosecond Ring Current Dynamics Joel Venzke, Cory Goldsmith, Agnieszka Jaron-Becker, Andreas Becker When a helium atom is excited into a superposition of a $1s$ and a $np+$ state, the electron wave packet produces a ring current with attosecond scale charge density dynamics. We have studied the preparation and time dependent imaging of such a system utilizing attosecond laser pulses. The presented results are obtained from {\it ab initio} simulations of the time dependent Schr\"{o}dinger equation in the single active electron and dipole approximations. Effects of pulse length, polarization and other parameters of the imaging pulse on the obtained data will be discussed. [Preview Abstract] |
Tuesday, May 28, 2019 3:12PM - 3:24PM |
D03.00007: Controlling ring currents in molecules Tennesse Joyce, Agnieszka Jaron-Becker The recent technological development of attosecond pulses with circular polarization may enable control over molecular ring currents. Besides having potential applications in nanoscale electronics and magnetism, ring currents may also be critical for quantitative, time-resolved studies of electron delocalization and aromaticity in molecules. In this talk, we introduce a control scheme whereby the dominant charge carriers for a molecular ring current can be chosen as either electrons or holes, depending on the intensity of the instigating laser pulse. As a proof-of-principle we have performed ab initio calculations using time-dependent density functional theory, which demonstrate control over ring currents in the benzene molecule by a few-femtosecond circularly polarized laser pulse. Additionally, we will discuss the role of symmetry breaking (i.e. the Jahn-Teller effect) in the subsequent field-free evolution of the molecular ring current. [Preview Abstract] |
Tuesday, May 28, 2019 3:24PM - 3:36PM |
D03.00008: Probing the dynamics of dark states using four-wave mixing processes in the XUV Nathan Harkema, Sergio Yanez-Pagans, Arvinder Sandhu Attosecond transient absorption spectroscopy (ATAS) has been used to probe ultrafast electron dynamics by measuring small changes in absorption of an extreme ultraviolet (XUV) pulse. Recently, this spectroscopic technique has been extended to implement four-wave mixing (FWM) between XUV and IR pulses. These FWM experiments can produce a background-free signal which is easier to detect and interpret than conventional ATAS. We show non-collinear FWM is ideally suited for studying optically dark states which do not appear in the XUV spectrum. By carefully tuning the XUV and IR photon energies, we can excite dark states as an intermediate step in the FWM process. We implement this scheme in Argon, which has a series of optically dark autoionizing states. With an appropriate pulse sequence, we use the FWM signal to obtain the lifetimes of these dark states. [Preview Abstract] |
Tuesday, May 28, 2019 3:36PM - 3:48PM |
D03.00009: XUV -- UV spectroscopy in atoms and molecules. Gabriel karras A novel experimental approach employing XUV and UV femtosecond pulses is presented and applied to the study of ultrafast physical processes in atomic and molecular targets in the gas phase. In particular, we report on the resonant pulse propagation of XUV pulses in He atoms and on the photoemission time delay of nitrogen molecules. The propagation of light pulses with a spectrum containing resonant frequencies with the propagating medium can significantly reshape the pulse envelope, as long as the pulse duration is shorter than the lifetime of the excited states. Here we discuss the macroscopic propagation of a resonant XUV attosecond pulse train, APT, using photoelectron spectroscopy experiments. Our measurements show how the XUV propagation induces a phase accumulation that leads to a chirp of the emitted electron wave-packets on the attosecond timescale and to time-dependent structures on femtosecond timescale. Taking advantage of the limited spectral congestion provided by our scheme we also applied it on a molecular target and we demonstrated its applicability in the study of photoemission time delays. Specifically we report on the relative photoemission time delay from the first two bound states of N$_{\mathrm{2}}^{\mathrm{+}}$, namely A and X. [Preview Abstract] |
Tuesday, May 28, 2019 3:48PM - 4:00PM |
D03.00010: Electronic Population Transfer via Impulsive Stimulated X-ray Raman Scattering Jordan O'Neal, Razib Obaid, Elio Champenois, Christoph Bostedt, James Cryan Impulsive stimulated X-ray Raman scattering (impulsive SXRS) has been proposed as a technique to prepare an electronic wavepacket in a molecular system. However, to leverage this method, impulsive SXRS must be experimentally established. To this end, we performed an experiment at the Linac Coherent Light Source (LCLS) in NO pumped by broad bandwidth (\textasciitilde 6 eV) attosecond X-ray pulses generated via the Enhanced SASE technique. Excited state neutral molecules were probed with a 266 nm UV laser pulse. Using a time-of-flight ion spectrometer we found increased NO$+$ production of \textasciitilde 5{\%} with a delayed probe laser relative to the inverse arrangement. This signal increases with pulse energy and only appears near the 1s-\textgreater $\pi $* resonance. [Preview Abstract] |
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