Angular distribution of relativistic electrons in the tunneling ionization of atoms by an ac field

We studied theoretically the influence of relativistic effects on the angular distribution of electrons in the tunneling ionization of atoms by a field of a linearly polarized electromagnetic wave. It was shown that the angular distribution is strongly asymmetric with respect to the direction of laser polarization. This asymmetry grows with the increasing of the relativistic energy of ejected electrons. The case of circular polarization is also considered.