Relativistic theory of the above-threshold multiphoton ionization of hydrogen-like atoms in the ultrastrong laser fields

The relativistic theory of above-threshold ionization (ATI) of hydrogen-like atoms in ultrastrong radiation fields, taking into account the photoelectron induced rescattering in the continuum spectrum is developed. It is shown that the contribution of the latter in the multiphoton ionization probability even in the Born approximation by Coulomb field is of the order of ATI probability in the scope of Keldysh-Faisal-Reiss ansatz.