NONPERTURBATIVE TIME-DEPENDENT THEORY AND ATI IN 2-ELECTRON ATOMS

This work deals with the fundamental problem of the behaviour of the t wo-electron atom under intense laser fields; i.e. (the three-body Coul omb problem under strong excitation. We present a broad scope of calcu lations and results and, we believe, the first ATI spectrum, in a thre e-dimensional atom, beyond the single active electron model in a fully time-dependent non-perturbative calculation. We perform calculations both on a two-electron basis with the configuration interaction where both electrons are allowed to be excited and on a frozen-core (single active electron) basis. The comparison is a direct measure of the effe ct of correlation under strong fields and the results open the way to the study of other atoms with much stronger correlation.