EXCITATIONS OF ATOMS WITH ELECTRONS IN A STRONG LIGHT-FIELD

The excitation of atoms with electrons in a strong light field is analyzed involving virtual photon absorption with a target. In the low frequency approximation the method is developed for calculating the excitation cross sections, based on using the average of instantaneous rate of the process over the external field period. For weak fields of frequencies comparable to the atomic transition frequency of an atom, the generalized Bethe - Born formula is obtained in the terms of expansion in powers of the external field strength.