Ab initio study of time-dependent dynamics in strong-field triple ionization

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Ab initio study of time-dependent dynamics in strong-field triple ionization

Jan H. Thiede, Bruno Eckhardt, Dmitry K. Efimov, Jakub S. Prauzner-Bechcicki, and Jakub Zakrzewski

Phys. Rev. A 98, 031401(R) – Published 7 September 2018

Abstract

An ab initio analysis of strong-field three-electron ionization in a restricted-dimensionality model reveals the dynamics of the ionization process and the dominant channels for double (DI) and triple ionization (TI). Simulations using wave functions that respect the Pauli principle show that the most likely channel is a sequence of single ionization (SI) and DI, while direct TI has a much lower probability. The dominant DI process has the highest probability for a singlet of up- and down-spin electrons. The results demonstrate the significance of the Pauli principle for the selection of dominant pathways in ionization and possibly other many-electron processes in strong fields.

Received 20 April 2018
Revised 10 July 2018

DOI:https://doi.org/10.1103/PhysRevA.98.031401

Physics Subject Headings (PhySH)

Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Photoemission Ultrafast phenomena

Atomic, Molecular & Optical

Authors & Affiliations

Jan H. Thiede and Bruno Eckhardt

Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany

Dmitry K. Efimov, Jakub S. Prauzner-Bechcicki, and Jakub Zakrzewski^*

Instytut Fizyki im. Mariana Smoluchowskiego, Uniwersytet Jagielloński, Łojasiewicza 11, 30-348 Kraków, Poland

^*jakub.zakrzewski@uj.edu.pl

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Vol. 98, Iss. 3 — September 2018

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Images

Figure 1
Division of the position space for the calculation of the ion yields (only the first octant is shown). Region 0 (neutral atom) is the volume bounded by the yellow, orange, and red planes. Region 1 (singly ionized atom) is the union of the six volumes bounded by the yellow, cyan, and blue planes. Region 2 (doubly ionized atom) is the union of the 12 volumes bounded by the orange, blue, and gray planes. Region 3 (triply ionized atom) is the union of the eight volumes bounded by the red, cyan, and gray planes. The missing boundary planes of regions 1–3 are given by the absorbing boundary (not shown).
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Figure 2
Numerical ionization yields for a two-cycle pulse as a function of top electric field amplitude in atomic units. $F_{0} = 0.1$ a.u. corresponds to $5.14 \times 10^{10}$ V/m and laser intensity $I = 3.5 \times 10^{14} W / {cm}^{2}$ . Left panel: Total yields (probabilities) for single ionization (SI, black circles), double ionization (DI, red triangles), and triple ionization (TI, green squares). The continuous lines are from the model, and dashed-dotted lines after integration over a Gaussian beam (9). SI saturates over a wide range of field strengths and DI shows a pronounced knee structure, TI a weak one. Right panel: Different contributions to DI and TI, over a smaller range of field amplitudes. The red dashed lines show the nonsequential double-ionization (NSDI) contribution to DI, which is overtaken by sequential processes for higher intensities. The legend identifies four contributions to TI, with the sequential process being the dominant and direct TI the weakest contribution.
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Figure 3
Spin-resolved time dependence of different ionization processes for $F_{0} = 0.15$ and $φ = 0$ . The left column shows contributions to SI and DI, and the right column to TI. (a) shows the pulse shape. (b) SI (black line) is dominated by $U$ electron emission (red dashed), while ionization of the $D$ electron (green dashed) has a much smaller probability. (c) shows that sequential double ionization (SDI) (black line) is composed of the dominant 0- $U - D$ channel (green dashed-dotted), with only small contributions from the 0- $U - U$ channel (red dashed line) and minor contributions from the path 0- $D - U$ (orange) in which the $D$ electron is ejected first. For NSDI (d) shows that the product $D U$ (green dashed-dotted) is strongly favored compared to $U U$ emission (red-dashed) – with black line giving the total NSDI. In the right column, (e) shows contributions to TI: sequential TI (STI) 0-1-2-3 (cyan), 0-2-3 channel (black), 0-1-3 (red dashed line), and 0-3 (green dashed line). (f) resolves the spin contributions to STI, with black, red-dashed, and green dotted-dashed curves corresponding to $U - U - D, U - D - U$ , and $D - U - U$ sequential emissions. (g) resolves the 0-2-3 DI followed by a single emission channel, and shows that the $D U - U$ path (red) is more prominent than the $U U - D$ sequence (black); (h) for the 0-1-3 channel the first SI is predominantly via the $U$ electron followed by the $U D$ pair (black) while $D - U U$ (green dashed) is negligible.
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Figure 4
The dependence of different ionization yields (indicated in the figure) on the carrier envelope phase $φ$ in Eq. (4). The data correspond to $F_{0} = 0.15$ . Observe that the importance of different paths for triple ionization may depend on $φ$ .
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