Двойная трехфотонная ионизация атомов с формированием промежуточного поляризованного иона

Sequential double three-photon ionization of atoms is one of nonlinear processes caused by pulses of X-ray or vacuum-ultraviolet radiation from free electron laser. Theoretical description for the phenomenon is developed within the dipole approximation and the second order perturbation theory. Cross section of the double three-photon ionization and the photoelectron angular distributions are obtained for the neon atom. Keywords: nonlinear processes, X-ray and vacuum-ultraviolet radiation, spectroscopy, atomic and ionic photo ionization.