New effects in the multiphoton ionization of atoms

The review is devoted to new effects discovered recently in the course of studying the process of nonlinear ionization of atoms in the field of laser radiation–above-threshold ionization, manifestation of multielectron structure of complex atoms, formation of multiply charged ions, tunneling ionization, and emission of short-wavelength radiation. The main experimental data and their theoretical interpretation are presented. A discussion is given of the criteria for the applicability of the lowest non-vanishing order of non-steady-state perturbation theory to the description of the interaction of an atom with the electromagnetic field.