Thin films of Ge30Se50Te20 with thickness of 100, 150, 200 and 250 nm were prepared by thermal evaporation technique on glass substrates.Normalincidence optical transmission spectra have been measured in the range from 190 to 900 nm.The optical constants were calculated using Swanepoel's method.The effect of film thickness on the optical constants had been investigated.Analysis of the refractive i...