Laser-induced nonsequential double ionization approaching the relativistic regime

Nonsequential double ionization of helium is investigated in such intense laser pulses that the mean electron wavepacket is driven to a velocity being non-negligible as compared to that of light. The known mechanism of nonsequential double ionization may change qualitatively as the recolliding (first ionized) electron may miss the ionic core with the inner electron due to the magnetically induced Lorentz force. We show that there is an intermediate regime beyond the dipole approximation with a reduced likelihood of double ionization via recollisions and we evaluate the modifications in the angular distribution of the yield of nonsequential double ionization.