Ionization and excitation of the excited hydrogen atom in strong circularly polarized laser fields

Abstract

In the recent work of Herath et al. [Phys. Rev. Lett. 109, 043004 (2012)] the first experimental observation of a dependence of strong-field ionization rate on the sign of the magnetic quantum number m (of the initial bound state (n,l.m)) was reported. The experiment with nearly circularly polarized light could not distinguish which sign of m favors faster ionization. We perform ab initio calculations for the hydrogen atom initially in one of the four bound sub states with the principal quantum number n=2 and irradiated by a short circularly polarized laser pulse of 800nm. In the intensity range of 10^12 to 10^13 Watts/cm^2 excited bound states play a very important role, but also up to some 10^15 Watts/cm^2 they can not be neglected in a full description of the laser-atom interaction. We explore the region that with increasing intensity switches from multiphoton to over the barrrier ionization and we find unlike in tunneling-type theories, that the ratio of ionization rates for electrons initially counter-rotating and co-rotating (with respect to the laser field) may be higher or lower than one.