Above-barrier ionization and quantum interference in strong laser fields

Classical predictions of field ionization of hydrogen and of Coulomb scattering in strong laser fields are compared with corresponding exact numerical solutions of the time-dependent Schr?dinger equation. In the quasi-static approximation, ionization rates are significantly lower than the quasi-classical tunneling rates in the regime of above-barrier ionization. This reduction is consistent with a simple classical barrier-suppression model. In time-periodic fields, the major differences between the classical and quantum-mechanical treatments arise from quantum-mechanical interference oscillations. These are typical for tunneling barriers in an applied field and for scattering by an oscillating potential. Received: 3 November 1999 / Published online: 30 June 2000