Thickness-dependent optical properties and nonlinear refractive index of a-Ge-Se-In thin films

The present work reports the study of linear optical properties of a-Ge20Se80-xInx (x = 0, 5, 10, 15, 20) system as a function of film thickness and at different Se/In ratio using transmission spectra. Optical gap increases with the increase in film thickness, whereas no significant change is found in the linear refractive index for all the compositions. To evaluate their potential applications for all-optical ultrafast switching devices, we report the effect of In alloying on the nonlinear refractive index and third-order susceptibility (chi((3))), evaluated from the changes of index of refraction using Wang approximations. Comparative higher values of susceptibility of the order of 10(-11) (in esu) are found and show a maximum at In = 10 at.%. The largest value of susceptibility can be expected for materials with higher values. Different formulations were used to predict the nonlinear behavior of Ge-Se-In system. The addition of In to Ge20Se80-xInx glass leads to an increase in the nonlinear refractive index, almost 500times that of fused silica. A comparison of our results shows a good agreement with values available in the literature. High nonlinearity of Ge-Se-In glasses makes them suitable for optical generation and Raman amplification.