Stabilization of atoms in superintense laser fields

The one-dimensional delta-function atom subject to a laser field is investigated in the regime of ultrahigh laser intensity. Stabilization is found in the sense that for sufficiently high intensity, the ionization probability becomes a decreasing function (on average) of the laser amplitude and may reach a level below 90%. Detailed intensity scans reveal the relevance of ponderomotive effects and allow a discussion of the criteria determining the onset of stabilization. A simple high-intensity approximation compares well with the exact numerical results, enabling an estimate of the optimal pulse turn-on time. Its success points to a mainly classical origin of stabilization and leads to the conclusion that the survival probabilities will be much lower for three-dimensional atoms. Its application to hydrogen leads to a significantly lower ground-state probability than obtained in a recent numerical study by Horbatsch, Tang and Basile (1991) confirming that localization is more likely to occur in 3D than in 1D.