Two‐Photon Absorption via Deep Local Levels as Virtual Intermediate States in Semiconductors

Abstract

AbstractThe enhancement of the coherent nonlinear losses are observed in ZnO and ZnSe crystals within the whole range of the interband two‐photon absorption (TPA) spectra. The effect is explained theoretically in terms of nonresonant participation of the deep local levels (DL) of impurities and native defects in the forbidden gap as additional intermediate virtual states of TPA. Calculations of interband TPA via DL including the influence of the momentum indeterminacy in local states are presented. The role of spatial interference of virtual contributions of the localized intermediate states in the momentum conservation is revealed. The possibility of the technological control of the additional nonlinearities is shown experimentally. The place of these phenomena among the widely investigated processes of coherent TPA via band states and the incoherent two‐step absorption through DL are discussed.