Magnetic-field-induced enhancement of atomic stabilization in intense high-frequency laser fields

Abstract

The role of the magnetic-field component of the laser pulse on the phenomenon of atomic stabilization is investigated in an ab initio study. This is achieved by solving the time-dependent Schr\"odinger equation for the laser-atom interaction beyond the dipole approximation. The system under study is atomic hydrogen and the atom is assumed to be irradiated by an intense xuv laser light pulse of varying intensity and duration. We consider two different photon energies, $\ensuremath{\hbar}\ensuremath{\omega}=54$ and 95 eV. The main finding is that there exists a range of laser pulse durations lasting for a few tens of field cycles where the atomic stabilization effect is enhanced due to the magnetic-field component. This is a rather surprising result that contradicts earlier statements made in the few-cycle pulse regime, where it has been shown that the magnetic field has a destructive effect in that the degree of stabilization is suppressed. It is further found that in the long-pulse limit the ionization probabilities obtained when illuminating the target with dipole and nondipole fields eventually coincide, meaning that the magnetic-field component of the laser field finally loses its significance in the context of atomic stabilization. It is also found that within the window of enhanced stabilization, the surplus population is distributed among excited bound states rather than in the initial ground state.