Nonlinear far-infrared absorption in InSb at light impact ionization

Abstract

A highly nonlinear far-infrared free-carrier absorption, rising with the radiation intensity, has been observed in InSb. It is shown that the nonlinearity arises from an increase in the number of free carriers caused by the generation of electron-hole pairs by light impact ionization in the radiation field of a powerful far-infrared laser. The observed nonlinearity permits the investigation of the process of impact ionization by a contactless optical method.