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Physical Review A

Towards atom-scale spin-selective electron emitters based on strong-field Freeman resonant ionization

Shengliang Xu, Qingbin Zhang, Xianglong Fu, Xiang Huang, Han Xu, Min Li, Wei Cao, Peixiang Lu

Published Dec 31, 2020• 10 citations
Publisher

Abstract

To produce electrons with well-defined spin via photoionization, realizing orbital-resolved ionization is the prerequisite due to spin-orbital coupling. In this paper, we numerically and experimentally demonstrate that the electrons emitted from two original energy degenerated orbitals ($j=3/2, m=1$ and $j=3/2, m=\ensuremath{-}1$) of Xe atoms can be well separated in the energy domain through selectively achieving Freeman resonance during strong-field ionization using a circularly polarized laser field. This orbital resolved Freeman resonant ionization leads to strong spin sensitivity without the need of fine laser frequency and intensity tuning. This result enables the production of high-degree spin-polarized electrons by energy gating, which provides a unique degree of freedom for advancing many promising applications.

DOI
10.1103/physreva.102.063128

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We show how spin polarization of photoelectrons produced in strong-field ionization of noble-gas atoms can be used to detect highly unexpected electron orbits created in strong, circularly polarized near-infrared fields. In such fields, ionization is expected to generate photoelectrons rapidly moving away from the ionic core, freezing their initial spin due to the short-range nature of the spin-orbit interaction between the photoelectron and the core. However, we find clear evidence of spin flips in the photoelectron spectra at low photoelectron energies and confirm that they happen because a photoelectron has been trapped near the core. The presence of such highly unexpected orbits explains the marked deviations between the recent experimental measurements of spin polarization [Nat. Photonics 10, 526 (2016)NPAHBY1749-488510.1038/nphoton.2016.109] and simulations with frozen spin.
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