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

The present paper reports the nonlinear optical properties of chalcogenide Se85-x Te15Bi (x) (0 a parts per thousand currency sign x a parts per thousand currency sign 5) thin films. The formulation proposed by Boling, Fournier, and Snitzer and Tichy and Ticha has been used to compute the nonlinear refractive index n (2). The two-photon absorption coefficient beta (2), and first- and third-order susceptibilities [chi ((1)) and chi ((3))] are also reported. The nonlinear refractive index n (2) is well correlated with the linear refractive index n and Wemple-DiDomenico (WDD) parameters, in turn depending on the density rho and molar volume V (m) 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 E (g), are measured experimentally using ellipsometric curves obtained by spectrophotometry. The composition-dependent behavior of n (2) is analyzed on the basis of various parameters, viz. density, bond distribution, cohesive energy (CE), and optical bandgap E (g), of the system. The variation of n (2) and beta (2) with changing bandgap E (g) is also reported. The values of n (2) and chi ((3)) of the investigated chalcogenides are compared with those of pure silica, oxide, and other Se-based glasses.