Above-threshold ionization of atoms in linearly polarized laser fields of relativistic intensities

Abstract

Within the framework of the relativistic quantum theory the multiphoton above-threshold ionization (ATI) of hydrogenlike atoms in the field of super-strong electromagnetic radiation of linear polarization, taking into account the photoelectron stimulated bremsstrahlung (SB) on the residual ion, is investigated. The latter is considered in the Born approximation by the Coulomb field which allows us to simplify the previous results in the generalized eikonal approximation upon the scattering potential and obtain an analytic formula for the relativistic ATI rate summed over the intermediate transitions of a photoelectron through the virtual states of the atomic continuum. The energetic spectra and angular distributions of photoelectrons are obtained with the secondary SB of photoelectrons. Due to the latter the partial ATI rates are 4 times larger than the ATI rates of the direct process. In contrast to the nonrelativistic case, the main peaks in the angular distributions of photoelectrons are shifted toward the wave propagation direction and have a tendency to be aligned about this direction with the increase of the field intensity.