Enhanced polarization transfer to the characteristic $L\alpha$ x-ray lines near the nonlinear Cooper minimum of two-photon ionization

TL;DR

This paper demonstrates that polarization transfer during two-photon ionization is significantly enhanced near the Cooper minimum, enabling detection of linear polarization in x-ray fluorescence lines using current free-electron laser technology.

Contribution

It introduces the concept of enhanced polarization transfer at the Cooper minimum in two-photon ionization and proposes an experimental setup with tungsten atoms to observe this effect.

Findings

Linear polarization transfer is strongly enhanced at the Cooper minimum.

Detection of polarization transfer is feasible with current free-electron laser facilities.

Proposed experiment involves two-photon ionization of tungsten's 2p_{3/2} electrons.

Abstract

It has been shown that for nonlinear atomic ionization, transfer of the degree of circular polarization from incident to fluorescence light is maximum at the Cooper minimum (see Phys. Rev. A \textbf{100}, 011401(R) (2019)). Until the present, however, it is still a challenge to produce and detect circularly-polarized light at xuv and x-ray photon energies. We here show, that transfer of linear polarization is strongly enhanced at the Cooper minimum in two-photon ionization and can be readily detected using current free-electron laser facilities by measurements of the degree of linear polarization of the characteristic $L\alpha_1$ and $L\alpha_2$ lines. Two-photon ionization of $2p_{3/2}$ electron of tungsten atom is proposed to demonstrate the presented phenomena and realization of such experiment is discussed in detail.