2-PHOTON DOUBLE-IONIZATION OF HE AND H-

Two-photon absorption processes resulting in two-electron ionization o f He and Hare calculated using a time-dependent close-coupling expansi on on a two-dimensional radial lattice. The ground state atom or ion i s subjected to a 10-cycle pulse of linearly polarized light with peak intensities ranging from 10(13) to 10(16) W cm(-2). Probabilities are calculated for one-photon single ionization, two-photon single ionizat ion and two-photon double ionization. The ratio of non-sequential doub le ionization to single ionization following two-photon absorption is found to be somewhat larger than the similar ratio following one-photo n absorption.