Nondipole effects in photon emission by laser-driven ions

The influence-of the magnetic-field component of the incident pulse on the emission of photons by multiply charged ions interacting with intense, near-infrared laser pulses is investigated theoretically using a strong-field approximation that treats the coupling of the atom with the incident field beyond the dipole approximation. For peak pulse intensities approaching 10(17) W cm(-2), the electron drift in the laser propagation direction due to the magnetic-field component of the incident pulse strongly influences the photon emission spectra. In particular, emission is reduced and the plateau structure of the spectra modified, as compared to the predictions in the dipole approximation. Nondipole effects become more pronounced as the ionization potential of the ion increases. Photon emission spectra are interpreted by analysing classical electron trajectories within the semi-classical recollision model. It is shown that a second pulse can be used to compensate the magnetic-field induced drift for selected trajectories so that, in a well-defined spectral region, a single attosecond pulse is emitted by the ion.