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

TL;DR

This study investigates how the ionization rates of excited hydrogen atoms in strong circularly polarized laser fields depend on the magnetic quantum number, revealing complex behaviors across different intensity regimes.

Contribution

It provides ab initio calculations showing the influence of initial quantum states on ionization rates, highlighting the importance of excited states and intensity effects in strong-field ionization.

Findings

Ionization rate ratios can be greater or less than one depending on initial state and intensity.

Excited bound states significantly affect ionization dynamics in strong laser fields.

Transition from multiphoton to over-the-barrier ionization occurs within the studied intensity range.

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.