Study of the circular dichroism of He+ ion

Abstract

We study the mechanism of circular dichroism (CD) in He+ under XUV and NIR pulses in the experimental condition presented by Ilchen et al. [Phys. Rev. Lett. 118, 013002 (2017)] and in a range of pulse intensities and durations by solving the time-dependent Schrodinger equation (TDSE) in momentum space. The method enables investigation of the ionization and intermediate transition probabilities of He+ in detail. We show that the lowest-order perturbation theory (LOPT) is qualitatively sufficient to describe experimental results and find that ionization favors co- and counter-rotating pulses for NIR intensities in and beyond LOPT regimes, respectively. In the experimental pulse duration, we show that a sub-peak along the first above-threshold ionization peak exists in the counter-rotating case due to one-photon absorption from excited states, which cannot be obtained by solving TDSE with a short duration of 22 fs, since the energy band width is too wide to resolve this substructure. We present the variation of CD values with NIR intensities. (C) 2019 Optical Society of America