Dichroism in the above-threshold two-colour photoionization of singly charged neon

In this work we report on the ionization of a gaseous neon target by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. Applying energy-resolved photoelectron spectroscopy, the dependence of the electrons ejected from singly charged neon (Ne+) on the relative polarization of the XUV and optical laser fields was investigated. The electron spectra exhibit a strong dependence on the degree of the relative orientation of the linear polarization vectors. A quantitative analysis was undertaken using multichannel time-dependent perturbation theory in order to reproduce the magnitude of the ejected low kinetic energy electrons as a function of the relative polarization directions and explicitly taking into account the influence of the residual Ne2+ cores (D-1, P-3). It is concluded that the variation of the photoelectron spectrum with the deviation of XUV and optical field directions is mainly related to the different responses of the magnetic substates of the ejected electrons in their interaction with the laser field.