Radiation pressure in SFA theory: retardation and recoil corrections

Radiation pressure effects in ionization by short linearly-polarized laser pulses are investigated in the framework of strong-field approximation, in both nonrelativistic and relativistic formulations. Differences between both approaches are discussed, and retardation and recoil corrections are defined. It is demonstrated how these corrections can be incorporated into the nonrelativistic approach, leading to the so-called quasi-relativistic formulation. These three approaches are further applied to the analysis of signatures of radiation pressure in energy-angular distributions of photoelectrons. It is demonstrated that, for Ti:Sapphire laser pulses of intensities up to $10^{16}\mathrm{W/cm}^2$, predictions of the quasi-relativistic formulation agree well with those of the full relativistic one, and that the recoil corrections contribute predominantly to the radiation pressure effects.