Photoinduced changes in optical properties of Ga–Sb–Ge–Se glasses

The kinetics of photoinduced effects on Ga5Sb10Ge25Se60 thin film exposed to continuous wave laser radiations are studied as a function of exposure time and laser intensity. The transmission and reflection spectra of thin films before and after exposure are investigated. The optical band gap and the refractive index are derived from the above spectra. Generalized Miller's rule and linear refractive index are used to find the nonlinear susceptibility and nonlinear refractive index of the thin films. The studies show a red shift in the band gap with increase in exposure time and laser power which is attributed to the photoinduced darkening in the films.