Interband phototransitions involving free electrons: Part II. Crystals with an indirect band gap

Nonlinear absorption of laser radiation with a photon energy lower than the indirect band gap of crystal has been considered. It is shown that, as in the case of direct-gap materials, single-photon resonance at the transitions between two conduction bands even at radiation intensities j ?? 10⁵?C10⁶ W/cm² yields a range of j values where optical absorption and concentration of nonequilibrium electron-hole pairs increase very sharply with an increase in j.