Strong-field effects in electron spectra from multiphoton ionisation

The energy spectrum of electrons resulting from multiphoton ionisation is analysed with the help of a simple, exactly soluble model. The weakening of lower energy lines with the increase in laser intensity, observed in experiments, occurs as a strong-field effect. The dependence of the light shift and the light broadening on the laser intensity and on the virtual-bound transitions in the atom are also analysed.