Relativistic effects in photoionizing a circular Rydberg state in the optical regime

Abstract

We study the photoionization process of a hydrogen atom initially prepared in a circular Rydberg state. The atom is exposed to a two-cycle laser pulse with a central wavelength of 800 nm. Before the atom approaches saturation, at field intensities of the order of 1017 W/cm2, relativistic corrections to the ionization probability are clearly seen. The ionization is predominantly driven by the radiation pressure in the propagation direction of the laser field, not by the electric field. Direct comparisons with the full numerical solution of the timedependent Dirac equation demonstrate quantitative agreement with a semi-relativistic approximation, which is considerably easier to implement.