Selectivity of Electronic Coherence and Attosecond Ionization Delays in Strong-Field Double Ionization

Yuki Kobayashi, Maurizio Reduzzi, Kristina F. Chang, Henry Timmers, Daniel M. Neumark, and Stephen R. Leone

Phys. Rev. Lett. 120, 233201 – Published 4 June 2018

Abstract

Experiments are presented on real-time probing of coherent electron dynamics in xenon initiated by strong-field double ionization. Attosecond transient absorption measurements allow for characterization of electronic coherences as well as relative ionization timings in multiple electronic states of ${Xe}^{+}$ and ${Xe}^{2 +}$ . A high degree of coherence $g = 0.4$ is observed between ${{}^{3}P}_{2}^{0} − {{}^{3}P}_{0}^{0}$ of ${Xe}^{2 +}$ , whereas for other possible pairs of states the coherences are below the detection limits of the experiments. A comparison of the experimental results with numerical simulations based on an uncorrelated electron-emission model shows that the coherences produced by strong-field double ionization are more selective than predicted. Surprisingly short ionization time delays, 0.85 fs, 0.64 fs, and 0.75 fs relative to ${Xe}^{+}$ formation, are also measured for the ${}^{3}{P_{2}}$ , ${}^{3}{P_{0}}$ , and ${}^{3}{P_{1}}$ states of ${Xe}^{2 +}$ , respectively. Both the unpredicted selectivity in the formation of coherence and the subfemtosecond time delays of specific states provide new insight into correlated electron dynamics in strong-field double ionization.

Received 26 February 2018
Corrected 28 September 2018

DOI:https://doi.org/10.1103/PhysRevLett.120.233201

Physics Subject Headings (PhySH)

Multiphoton or tunneling ionization & excitation Ultrafast phenomena

Atoms

High-harmonic generation

Atomic, Molecular & Optical

Corrections

28 September 2018

Correction: The omission of a contract number in the Acknowledgments section has been fixed.

Authors & Affiliations

Yuki Kobayashi^1,*, Maurizio Reduzzi¹, Kristina F. Chang¹, Henry Timmers¹, Daniel M. Neumark^1,2,†, and Stephen R. Leone^1,2,3,‡

¹Department of Chemistry, University of California, Berkeley, California 94720, USA
²Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
³Department of Physics, University of California, Berkeley, California 94720, USA

^*ykoba@berkeley.edu
^†dneumark@berkeley.edu
^‡srl@berkeley.edu

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Vol. 120, Iss. 23 — 8 June 2018

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Images

Figure 1
(a) Schematic of the experimental setup. The red beam represents few-cycle NIR pulses, and the blue beam represents attosecond XUV pulses. AF, aluminum filter; BS, beam splitter; CG, concave grating; FM, focusing mirror; GC1, gas cell for high-harmonic generation; GC2, gas cell for absorption measurements; TM, toroidal mirror; XC, x-ray camera. (b) Energy-level diagram of ${Xe}^{n +}$ ( $n = 0$ , 1, 2, 3). The $5 p$ electrons of xenon atoms are ionized by the strong NIR pulses (orange arrows), and the subsequent attosecond XUV pulses excite the $4 d$ electrons to the $5 p$ holes (vertical arrows). (c) Experimental transient absorption spectrum (gray area, right axis) and calculated oscillator strengths for the $4 d − 5 p$ transitions of ${Xe}^{n +}$ ( $n = 1$ , 2, 3) (green, red, blue lines, left axis). (d) Fine energy structure of the $(5 p)^{- 2}$ electronic configuration. The numbers in brackets denote relative energy from the lowest ${}^{3}{P_{2}}$ state in units of eV.
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Figure 2
(a) Experimental delay-dependent transient absorption spectra. The duration and the peak field intensity of the NIR pump pulse are 3.5 fs and $7 \times 10^{14} {W / cm}^{2}$ . (b) Fourier transformation of the experimental results. Quantum beat signals with 1.0 eV frequency are seen at 56.9 eV, 58.0 eV, 58.3 eV, and 59.3 eV. (c) Simulated absorption spectra. The coherence is set between ${{}^{3}P}_{2}^{0} − {{}^{3}P}_{0}^{0}$ at $g = 0.4$ . (d) Fourier transformation of the simulated results. The experimental signals at 1.0 eV are well reproduced, and their assignments are given.
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Figure 3
(a)–(c) Core-to-valence absorption spectra computed for each state in the ${{}^{3}P}_{J}$ manifold (solid curves), plotted together with the experimental static transient absorption spectrum (gray area). The $m$ -sublevels of ${}^{3}{P_{2}}$ and ${}^{3}{P_{1}}$ are overlaid in the same graph. The gray arrows indicate the absorption peaks that are used to determine the time delay. (d)–(f) Lineouts of the experimental transient absorption signals (dots with error bars) and the error-function fittings (solid curves). The signal from the ${{}^{3}P}_{3 / 2}$ state of ${Xe}^{+}$ at 55.4 eV is shown in black, and the signals from each state in the ${{}^{3}P}_{J}$ manifold are shown with colors. The vertical bars in the curves indicate the center of the rise.
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Figure 4
(a) Simulated electronic coherences among the ${{}^{3}P}_{J}$ and ${{}^{2}P}_{J}$ manifolds with the experimental pump-pulse parameters. The gray curve shows the electric field of the pump pulse. The coherences $g$ after the ionization are denoted next to the state labels. (b) Simulated electronic populations and ionization time delays. The dotted curves represent the simulated evolution of populations, and solid curves represent fitting results with error functions that are used to extract the rise times. The vertical bars in the curves indicate the center of the rise. The ionization time delays are denoted next to the state labels.
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