Rydberg electrons in laser fields: A finite-range-interaction problem

Abstract

A theory of Rydberg and continuum states in intense laser fields is developed based on the observation that the effect of laser radiation can be described in a scattering formulation as a finite-volume interaction coupling Coulomb-type fragmentation channels. In particular, laser-induced couplings may be incorporated in a multichannel quantum-defect treatment, in which a set of dressed channels corresponding to different photon numbers is defined, with intensity-dependent quantum defects and mixing angles. These quantities may be obtained by solving a system of close-coupling equations for the electron wave function, in a frame where the asymptotic electron oscillations are transformed away. This allows us to read off at a finite distance a radiative reaction matrix, which is a smooth function of energy for an energy range small compared with the photon frequency, and contains the net effect of radiative couplings. Calculations are presented for ionization of hydrogen s states in circularly polarized laser light, with allowance for above-threshold photon absorption.