Progress in Ultrafast Intense Laser Science VII

We investigate ionization of Dirac hydrogen atom and hydrogenic ions of charge states Z using the relativistic intense-field theory of spin-resolved ionization process. We discuss the energy dependence, emission angle dependence, spin dependence and charge stateZ dependence of ionization rates for free-electron laser (FEL) and infrared frequencies. The results of relativistic intense-field model calculations are compared with the corresponding nonrelativistic calculations, and in specific cases also with the results of relativistic single-photon first Born approximation. Furthermore, we discuss two counterintuitive predictions made earlier: (a) an asymmetry of the up and down spin electron currents from unpolarized target H-atoms, and (b) an increase of the ionization probability with the increase of the ionization potential in certain domains of the charge states Z for a given laser intensity and frequency.