The optical properties of amorphous Ge x As x Se 2-x (x = 0.050.30) thin films prepared by thermal evaporation on glass substrates held at T substr = 100 o C are reported. The transmission spectra was used for the calculation of the absorption coefficient , optical band gap E g , and the values of the refractive index n. The dependences of , E g , and n on the film composition in the Ge x As x Se 1-2x glassy system were determined. It was established that the optical band gap E g decreases,

more »

... hile the refractive index n increases with increasing concentration of Ge and As in the Ge x As x Se 2-x glassy system. The time dependence of the transmission T(t) during the light exposure for the above band gap illumination (photodarkening) is described by a strength exponential behavior T(t)/T(0) = A 0 +Aexp[-(t-t 0)/τ] (1-) , where t is the exposure time, τ is the apparent time constant, A characterizes the exponent amplitude, t 0 and A 0 are the initial coordinates, and  is the dispersion parameter (0<<1).