Relativistic ionization of hydrogen by linearly polarized light.

Relativistic ionization of hydrogen by intense, linearly polarized light is treated by the Strong Field Approximation (SFA). Both bound and ionized states are described by the Dirac equation, with spin effects fully included. The applied laser field is also treated relativistically. There is no recourse to the dipole approximation nor to large-component, small-component approximations. Examples are calculated for the long-pulse limit of a uniformly distributed laser field. A prediction is verified that relativistic effects will appear with linear polarization of the laser at lower intensities than with circular polarization. Strong-field atomic stabilization is found to be enhanced by relativistic effects.