Structural and optical characterization of Ag photo-doped thin As40S60-Se-x(x) films for non-linear applications

This paper deals with the structure and the optical properties of thin As40S60-xSex films doped with silver. The refractive index n and the optical band gap E-g(opt) were calculated from the transmittance and reflectance spectra. The results showed that the photo-doping leads to increase in the refractive index by about 0.25-0.27. An effect of thickness expansion was observed in the photo-doped layers. The non-linear refractive index, gamma, and the two-photon absorption coefficient, beta, were evaluated by applying a formula developed by Sheik-Bahae. Each of the films studied exhibits a highly non-linear refractive index at the telecommunication wavelength, 70-850 times higher than that measured for fused silica. From the Raman spectra of thin As40S30Se30 it might be concluded that under dissolution, the silver interacts with both sulfur and selenium. The surface of the thin films was investigated by using a white light interferometric profiler. It was found that the increase in the thickness of the silver layer results in roughening of the surface of the photo-doped films.