Interaction of an atom with superstrong laser fields

A theory of atomic interaction with a superstrong laser field has been developed. The specific feature of the suggested theory is that its small parameter is the interaction between the atom and the solenoidal part of the external field, whereas its interaction with the potential part is accurately taken into account. It follows from the reported investigation that, in calculating the interaction of atoms with superstrong fields, one must abandon calculations of multipole moments of transitions between unperturbed atomic levels, and calculate instead the atomic response, which comprises multipole moments of all orders and depends on the instantaneous field magnitude. The results are compared with calculations based on the perturbation theory in terms of the interaction Hamiltonian. Zh. éksp. Teor. Fiz. 116, 793–806 (September 1999)