On the Theory of Interband Two-Photon Absorption of Light in Semiconductors. Accounting Admixtures to the States of the Conduction Band and Valence States, the Rabi Effect

We present a theoretical study of interband two‐photon (two‐quantum) absorption of polarized light in semiconductors of cubic and tetrahedral symmetry. Our analysis is conducted within a multiband approximation, taking into account the admixture of valence states in the conduction‐band states, as well as coherent saturation (Rabi) effects. We use simplified parabolic dispersion laws for both heavy‐ and light‐hole subbands and for the conduction band, and compare two common temperature‐dependent band‐gap formulas (Varshni and Passler) to illustrate how they alter the spectral–temperature dependence of the total two‐photon absorption coefficient. In particular, we show that the interband two‐photon absorption first increases with photon frequency, reaches a maximum, and then decreases at a fixed temperature. The amplitude of the absorption for linearly polarized light is found to be larger than that for circularly polarized light, especially at lower temperatures. Our calculations reveal that the admixture of valence states significantly modifies the interband transitions, while the Rabi effect reduces the absorption in the high‐intensity regime, especially at elevated temperatures. These findings may be useful for designing optoelectronic and photonic devices that rely on multiphoton interactions in narrow‐gap semiconductors.