Timing angular momentum transfer for parity-unfavored transitions in multiphoton ionization

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Timing angular momentum transfer for parity-unfavored transitions in multiphoton ionization

Meng Han, Hao Liang, Peipei Ge, Yiqi Fang, Zhenning Guo, Xiaoyang Yu, Yongkai Deng, Liang-You Peng, Qihuang Gong, and Yunquan Liu

Phys. Rev. A 102, 061101(R) – Published 3 December 2020

Abstract

When a bound electron is photoionized from an atom or molecule, the remaining multielectron ion with excess internal energy will relax towards lower-energy states. The subsequent transverse angular momentum transfer between the parent ion and the ejected electron can lead to an electron parity-unfavored transition. Here we perform a self-calibrated timing experiment to measure the time delay of the angular momentum transfer of parity-unfavored transitions during the multiphoton ionization. We use a strong linearly polarized 400-nm light field to trigger a parity-unfavored transition in the channel of the spin-orbit excited ionic state of krypton atoms and then selectively probe the phases of the electron wave functions with different magnetic quantum numbers with a weak parallelly (orthogonally) polarized 800-nm light field. The parallel and orthogonal probes serve as the start and the stop of a stopwatch, respectively. Hence, this allows us to access the characteristic time of such an ultrafast intra-atom multielectron process.

Received 24 June 2020
Revised 8 November 2020
Accepted 13 November 2020

DOI:https://doi.org/10.1103/PhysRevA.102.061101

Physics Subject Headings (PhySH)

Atomic & molecular processes in external fields Autoionization & Auger processes Multiphoton or tunneling ionization & excitation

Atomic, Molecular & Optical

Authors & Affiliations

Meng Han ¹, Hao Liang ¹, Peipei Ge¹, Yiqi Fang¹, Zhenning Guo¹, Xiaoyang Yu¹, Yongkai Deng¹, Liang-You Peng^1,2,4, Qihuang Gong^1,2,4, and Yunquan Liu^1,2,3,4,*

¹State Key Laboratory for Mesoscopic Physics, Frontiers Science Center for Nano-Optoelectronics, Collaborative Innovation Center of Quantum Matter, School of Physics, Peking University, Beijing 100871, China
²Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
³Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871, China
⁴Beijing Academy of Quantum Information Sciences, Beijing 100193, China

^*Yunquan.liu@pku.edu.cn

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Vol. 102, Iss. 6 — December 2020

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Images

Figure 1
Angular momentum transfer in the parity-unfavored photoionization of krypton atoms and the phase measurement with two-color fields. (a) Principle of measurement. When a krypton atom is ionized by a strong linearly polarized 400-nm light field (the pump), the first-order ATI from the channel of the $J_{i} = 1 / 2$ ionic state is formed by the resonance-assisted parity-unfavored transition where the electron angular momentum is transferred from $d_{0}$ to $d_{1}$ and $d_{2}$ . A parallel (or orthogonal) 800-nm light field is used to probe the phase of the electron wave packet populated at the $d_{0}$ (or $d_{2}$ ) state. The electron wave packet from the $J_{i} = 3 / 2$ ionic state serves as the phase reference, allowing one to calibrate the measured phase from the $J_{i} = 1 / 2$ channel. (b) Measured photoelectron momentum distribution in the pump light field polarized along the $z$ axis. There are two sets of ATI structures, corresponding to the two ionic states. The one with a lower energy is contributed from the $J_{i} = 1 / 2$ ionic state. (c) Photoelectron angular distribution of the first-order ATI from the $J_{i} = 1 / 2$ ionic state and its least-squares fitting with the $d_{0}$ , $d_{1}$ , and $d_{2}$ waves. The fitting result is $0 . 249 Y_{20} {(θ)}^{2} + 0 . 078 Y_{21} {(θ)}^{2} + 0 . 673 Y_{22} {(θ)}^{2}$ , where $Y_{l m} (θ)$ is the spherical harmonics and the photoelectron emitting angle is defined as $θ = arctan (p_{x} / p_{z})$ . As to the experimental curve, we integrated the photoelectron energy in the range of [0.2, 0.6] eV and performed the symmetrical operation in order to implement the fitting. (d) and (e) Phase-integrated photoelectron momentum distributions probed by a weak parallel (d) and orthogonal (e) linearly polarized 800-nm light fields. The blue and red arrows at the top-right corner mark the polarization directions of the 400-nm and 800-nm lights, respectively. The solid and dashed arrows mark the first-order ATI and the first-order sideband from $J_{i} = 1 / 2$ , respectively. In (b), (d), and (e), the photoelectron momentum $p_{y}$ along the light propagation direction was integrated in the range of [−0.2, 0.2] eV.
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Figure 2
Time-resolved angular distribution of the first-order sideband in the PTC fields. (a) and (b) Measured time-resolved photoelectron angular distributions from the (a) $J_{i} = 3 / 2$ and (b) $J_{i} = 1 / 2$ ionic states as a function of the phase delay between the two pulses. The photoelectrons are integrated in the energy range of [2.1, 2.7] eV for (a) and [1.4, 2.0] eV for (b). (c) Simulated time-resolved angular distribution of the $J_{i} = 3 / 2$ ionic state with the TDSE method. (d) Angle-resolved PP extracted from (a) and (b) using the Fourier transform.
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Figure 3
Time-resolved results of the first-order sideband in the OTC fields. Figure captions are the same as those in Fig. 2.
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Figure 4
(a) Phase difference between extracted PPs from the two ionic states. (b) Time delay from the resonance ( $τ_{res}$ ), the sum of $τ_{res}$ , and the time delay of the parity-unfavored transition ( $τ_{put}$ ), which are converted from the phase difference at the emitting angle of 0 ° in the PTC fields and at the angle of 90 ° in the OTC fields, respectively. The integration window of the electron emitting angle is 10 ° as illustrated by the shadows in (a). In (b), the original data are marked with blue diamonds and red circles, and the mean value and the standard deviation are represented by the black error bars.
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