Investigation of Optical Nonlinearities in Bi-Doped Se-Te Chalcogenide Thin Films

The present paper reports the nonlinear optical properties of chalcogenide Se85−xTe15Bix (0 ≤ x ≤ 5) thin films. The formulation proposed by Boling, Fournier, and Snitzer and Tichy and Ticha has been used to compute the nonlinear refractive index n2. The two-photon absorption coefficient β2, and first- and third-order susceptibilities [χ(1) and χ(3)] are also reported. The nonlinear refractive index n2 is well correlated with the linear refractive index n and Wemple–DiDomenico (WDD) parameters, in turn depending on the density ρ and molar volume Vm of the system. The density of the system is calculated experimentally by using Archimedes’ principle. The linear optical parameters, viz. n, WDD parameters, and optical bandgap Eg, are measured experimentally using ellipsometric curves obtained by spectrophotometry. The composition-dependent behavior of n2 is analyzed on the basis of various parameters, viz. density, bond distribution, cohesive energy (CE), and optical bandgap Eg, of the system. The variation of n2 and β2 with changing bandgap Eg is also reported. The values of n2 and χ(3) of the investigated chalcogenides are compared with those of pure silica, oxide, and other Se-based glasses.