Electron spectrum of atoms ionized by an ultrashort laser pulse of relativistic intensity

Energy transfer to electrons in atoms ionized by an ultrashort laser pulse of relativistic intensity ($I>$ 10$^{19}$ W/cm$^2$) is considered. The ionization process is taken into account using the mechanism of direct suppression of the Coulomb barrier in a laser field. The acceleration of electrons in the laser wave field is described in terms of the classical relativistic equation of motion. Electron energies in the final state are determined as dependent on the average intensity of a laser pulse with a given shape. A distribution of the final energies of electrons upon multiple ionization of a complex atom is found.