Integral-equation approach to multiphoton ionization by intense fields. II. Application to H andH−

We have developed an integral-equation method for treating multiphoton ionization of atomic systems irradiated by intense fields. We have applied this method to the calculation of partial rates for multiphoton detachment of ${\mathrm{H}}^{\mathrm{-}}$ (into specific continuum channels) by a laser operating at frequencies of 0.2 and 0.5 eV. Nonperturbative features are seen at intensities above about 5×${10}^{10}$ W/${\mathrm{cm}}^2$. We have also applied the method to hydrogen, to the determination of the field-induced width in the ground-state energy (the total ionization rate).