Theoretical study of multiphoton absorption of light in semiconductor crystals in the multiband approximation

The frequency dependence of the light absorption coefficient due to the successive absorption of two and three quantum associated with direct optical passages between the valence and conduction bands in crystals with narrow band has been studied. A calculation was carried out based on the perturbation theory in the Kane approximation, where we assume that the energy spectrum of electrons is spherically symmetric. A quantitative analysis of the frequency dependence of the three-photon absorption coefficients of radiation in semiconductors with narrow band has been carried out.