GREENS-FUNCTION THEORY OF MULTI-PHOTON IONIZATION

The semiclassical (dressed) one-particle Green's function method developed for electron scattering in the presence of a radiation field is applied to single- and multi-photon ionization of atoms. In this case, a semiclassical (dressed) one-particle Green's function (Gωion) is defined with respect to an ionic core state. We propose a systematic way to solve for Gωion perturbatively. When Gωion is obtained by this method in terms of the usual one-particle Green's function Gion, the effective dipole moments for single- and multi-photon processes (rωneff) which include virtual single- and multi-photon core excitation (or core polarization) effects are naturally and systematically derived. © 1979.