Nonlinear refractive index in thin GexSb40-xS 60 films

A suitable relationship between the linear n_L and the nonlinear refractive index n₂ has been used for prediction of the nonlinear behavior of the refractive index in thin Ge_xSb _40-xS₆₀ films. The parameters (linear refractive index n_L and the dispersion parameters E₀ and E _d) necessary for the calculation of the n₂ are studied by means of spectrophotometry in the light wavelength region of 0.5-2.5 μm. It has been established that the nonlinear refractive index increases with increasing linear refractive index. The obtained results for n_L and n₂ are considered in terms of the average coordination number Z. The observed peculiarity in the compositional dependences of the linear and nonlinear refractive indices around Z=2.65-2.67 can be connected with the structural changes associated with a topological phase transition of the film structure