Recollision as a probe of magnetic-field effects in nonsequential double ionization

Fully accounting for nondipole effects in the electron dynamics, double ionization is studied for He driven by a near-infrared laser field and for Xe driven by a mid-infrared laser field. Using a three-dimensional semiclassical model, the average sum of the electron momenta along the propagation direction of the laser field is computed. If nondipole effects are not accounted for, the average momentum of each electron in the propagation direction of the laser field is zero. When nondipole effects are accounted for the sum of the electron momenta is found to be an order of magnitude larger than twice the average electron momentum along the propagation direction of the laser field in single ionization. This average sum of the electron momenta is found to be maximum at intensities smaller than the intensities satisfying previously predicted criteria for the onset of magnetic- field effects. It is shown that strong recollisions are the reason for this unexpectedly large value of the sum of the momenta along the direction of the magnetic component of the Lorentz force.