Experimental Separation of Subcycle Ionization Bursts in Strong-Field Double Ionization of ${\mathrm{H}}_{2}$

Experimental Separation of Subcycle Ionization Bursts in Strong-Field Double Ionization of $H_{2}$

Václav Hanus, Sarayoo Kangaparambil, Seyedreza Larimian, Martin Dorner-Kirchner, Xinhua Xie (谢新华), Markus S. Schöffler, Gerhard G. Paulus, Andrius Baltuška, André Staudte, and Markus Kitzler-Zeiler

Phys. Rev. Lett. 124, 103201 – Published 12 March 2020

Abstract

We report on the unambiguous observation of the subcycle ionization bursts in sequential strong-field double ionization of $H_{2}$ and their disentanglement in molecular frame photoelectron angular distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase, in combination with multiparticle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-state-specific Coulomb distortions on emitted electrons in polyatomic molecules.

Received 18 September 2019
Accepted 10 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.103201

Physics Subject Headings (PhySH)

Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Photodissociation Strong-field-induced spectra Ultrashort pulses

Molecules

Atomic, Molecular & Optical

Authors & Affiliations

Václav Hanus ^1,*, Sarayoo Kangaparambil¹, Seyedreza Larimian¹, Martin Dorner-Kirchner ¹, Xinhua Xie (谢新华)^1,2, Markus S. Schöffler³, Gerhard G. Paulus⁴, Andrius Baltuška¹, André Staudte⁵, and Markus Kitzler-Zeiler ^1,†

¹Photonics Institute, Technische Universität Wien, A-1040 Vienna, Austria
²SwissFEL, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
³Institut für Kernphysik, Goethe-Universität, D-60438 Frankfurt am Main, Germany
⁴Institute for Optics and Quantum Electronics, Friedrich-Schiller-Universität Jena, D-07743 Jena, Germany
⁵Joint Attosecond Science Lab of the National Research Council and the University of Ottawa, Ottawa, Ontario K1A 0R6, Canada

^*vaclav.hanus@tuwien.ac.at
^†markus.kitzler-zeiler@tuwien.ac.at

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Vol. 124, Iss. 10 — 13 March 2020

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Figure 1
(a) Electric field $E (t)$ in the polarization plane of a pulse with $CEP = 0$ . The electric field $E (t_{i})$ and vector potential $A (t_{i})$ at the instant of the emission $t_{i}$ of an electron with momentum $p_{e i}$ are indicated. (b) Absolute value of the field evolution shown in (a), $| E (t) |$ . The red and blue areas, denoted $P_{1}$ and $P_{2}$ , sketch the single and double ionization rates, respectively, with the subcycle ionization bursts at the peaks of $| E (t) |$ (numbered 1–6). Two ionization instants delayed by $Δ t = 1.5 T$ with each other, marked by $❶$ and $❷$ , and the corresponding dominant directions of the $⊥$ momenta of the two emitted electrons $p_{e 1, ⊥}$ and $p_{e 2, ⊥}$ are indicated. (c) Potential energy curves of $H_{2}$ relevant for SDI with a delay $Δ t$ between the two ionization steps $❶$ and $❷$ . (d) Sketches of momentum vectors for three cases of SDI dynamics corresponding to the three lobes in (e), as indicated by arrows. (e) Measured recoil momentum vector $p_{rec} = p_{H^{+}} + p_{H^{+}} = - (p_{e 1} + p_{e 2})$ in the laser polarization plane perpendicular $⊥$ and parallel $∥$ to the main axis of the polarization ellipse, cf. (a). (f) $p_{rec, ⊥}$ vs KER. The upper and lower lobes from (e) appear as separated peaks $A / C$ and $A^{'} / C^{'}$ , respectively, and the center lobe appears as peak $B$ .
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Figure 2
Measured distributions of the recoil momentum vector along the minor polarization axis $p_{rec, ⊥}$ over CEP for the three indicated ranges of KER (in eV): (a) $13.6 < KER < 15.6$ , (b) $11.6 < KER < 13.6$ , and (c) $9.6 < KER < 11.6$ .
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Figure 3
(Top) Absolute value of electric field $| E (t) |$ (black) and simulated SDI rates (red, blue) over time for different values of the CEP and $Δ t$ (columns). (Bottom) Corresponding simulated electron momentum distributions in the polarization plane. See text for details.
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Figure 4
(a) Measured energy distribution of electrons for $Δ t = 1.5 T (\pm 0.25 T)$ ( $11.6 < KER < 13.6 eV$ , peak $B$ ) over CEP emitted into the hemisphere facing the detector. The average energy is shown by a red line. The blue line denotes the average energy emitted into the opposite hemisphere. (b),(c) Simulated subcycle emission bursts (reproduced from Fig. 3) for the same range of $Δ t$ as in (a) for two values of the CEP indicated by circles and arrows. The gray lines depict the electrons’ energy $\propto | A (t) |^{2}$ . The cartoons left [right] of (b) [(c)] visualize the corresponding momentum vectors of the two emitted electrons. The two possible cases in (c) are indicated by brown and green colors, respectively. (d) MF-PAD corresponding to (b). (e) MF-PAD corresponding to (c).
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Physical Review Letters

Experimental Separation of Subcycle Ionization Bursts in Strong-Field Double Ionization of H2

Václav Hanus, Sarayoo Kangaparambil, Seyedreza Larimian, Martin Dorner-Kirchner, Xinhua Xie (谢新华), Markus S. Schöffler, Gerhard G. Paulus, Andrius Baltuška, André Staudte, and Markus Kitzler-Zeiler

Phys. Rev. Lett. 124, 103201 – Published 12 March 2020

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Experimental Separation of Subcycle Ionization Bursts in Strong-Field Double Ionization of $H_{2}$