Photoionization by ultrashort pulses in the high-intensity limit

The ionization of one-electron model atoms interacting with an intense few-cycle laser pulse is calculated by integrating numerically the time-dependent Schrödinger equation. If the pulse is sufficiently intense and short, the electron behaves as if it were not interacting with the binding potential. The probability that the atom is ionized or is excited to a given bound state then depends only on the extent to which the electronic wave packet spreads during the pulse; in particular, it does not depend on the frequency or on the peak intensity. Calculations at 800 nm wavelength for a two-dimensional model of a circular state suggest, however, that radiation pressure is likely to prevent the observation of the effect in a real atom. At intensities below 1016 W/cm2, however, the main effect of the magnetic field component of the incident pulse is to redistribute the population among bound states, not to increase photoionization.SCOPUS: ar.j