Photon emission by ions interacting with short intense laser pulses: beyond the dipole approximation

Photon emission by light hydrogen-like ions interacting with intense, few-cycle Ti:sapphire laser pulses is calculated within the strong-field approximation of Lewenstein and co-workers, modified so as to treat the coupling of the atom with the incident field beyond the dipole approximation. The approach is tested by comparing with results obtained by solving the time-dependent Schrödinger equation numerically for a two-dimensional model ion. The effect of the magnetic field component of the driving pulse is significant beyond 2×10¹⁷ W cm^-2 peak intensity. It leads, in particular, to a saturation in photon emission with increasing laser intensity. As compared with emission polarized along the same direction as the incident field, emission polarized along its propagation direction is weaker by about two orders of magnitude at the maximum peak intensity considered, 3.6×10¹⁷ W cm^-2.