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The modification of the photoionization cross section due to the presence of an intense low-frequency laser is obtained for the hydrogen-atom target. Previous calculations of this effect have neglected the effects of the Coulomb potential in the final state. A sum rule was obtained which indicates that the photoelectric current is unaffected by the presence of the low-frequency laser to lowest order in the laser frequency. It is found that the Coulomb potential changes this result and that the photoelectric current is changed by a factor which depends upon the laser parameters and the electron momentum. A simple experiment is suggested to confirm this prediction.

When an electron scatters from an atom in the presence of a laser field which is resonant with an atomic transition, off-shell effects enter into the cross section. These only become significant at higher laser intensities where the atom may also be ionised by the laser. Cross-sections are obtained for electron-atom scattering in which these off-shell effects appear and in which the slow ionisation of the atom by the laser is included. Experiments are suggested in which simplifications can occur and which still retain these 'exotic' effects.