From the UV to the static-field limit: Rates and scaling laws for intense-field ionization of helium

We present high-accuracy calculations of ionization rates of helium at UV (195 nm) wavelengths. The numerical results are obtained from full-dimensional numerical integration of the two-electron time-dependent Schroedinger equation. Comparison is made between ionization rates at 195 nm with previously obtained data at 390 nm and 780 nm. In addition, we have obtained quantitatively accurate solutions of the full-dimensional time-dependent Schroedinger equation for static-field ionization of helium. We compare our numerically integrated rates with those of time-independent calculations, and obtain good agreement over a wide range of intensities.