We present the first quantitative results for the ionization of hydrogen at relatively high frequencies, from low intensities to superintensities in excess of the atomic unit ${\mathit{I}}_0$=3.51×${10}^{16}$ W/${\mathrm{cm}}^2$. We find that at superintensities the atom has a tendency to stabilize against multiphoton ionization, even at low frequencies. We show, however, the existence of very short lifetimes for the ground state, at intensities just below those needed for stabilization.

• Received 7 May 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.2362