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Studies on semiconducting chalcogenide glasses have received much attention because of their important optical application in IR region [1-6]. Impurity effects in chalcogenide glasses may have importance in the fabrication of glassy semiconductor devices. The most important application of chalcogenide glasses are now in the field of optics and arise chiefly from either their infrared transmitting properties or photo-induced effects exhibited by them. They have potential use in integrated optics, optical imaging, optical data storage and infrared optics [7–15]. The optical band gap, refractive index and extinction coefficient are the most significant parameters in amorphous semiconducting thin films. The optical behaviour of material is utilized to determine its optical constants. Films are ideal specimen for reflectance and transmittance type measurements. Therefore, an accurate measurement of the optical constant is extremely important. Chalcogenide glasses have been found to exhibit the change in refractive index under the influence of light, which makes it possible to use these materials to record not only the magnitude but also the phase of illumination. The later is especially important in holographic optical data storage and in the fabrication of various integrated components and devices such as selective optical filters, mixers, couplers and modulators [16-18]. Most of the work has been carried out on chalcogenide thin films having Te as a major constituent. One of the limitations of Te based materials is their poor oxidation resistance. Hence, attempts have been made to investigate Se based chalcogenide thin films. Se has been selected because …