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.
Categories: physics.atom-ph