Linear and nonlinear optical changes in amorphous As2Se3 thin film upon UV exposure

Amorphous As2Se3 chalcogenide thin film was exposed to UV light (i line and g line) using mercury lamp for 30 min. XRD, UV/VIS spectroscopy and thickness measurements were taken for unexposed and exposed thin film for structural and optical characterizations. Linear optical constants (linear refractive index, extinction coefficient and linear optical absorption coefficient) of the film were calculated from transmission spectra using Swanepoel method. Optical bandgap was determined using Tauc's relation of indirect bandgap material. Dispersion of the material was described by single-oscillator Wemple-DeDiDomenico model. Nonlinear optical constants (χ(3) and n2) were determined from linear optical parameters using semi-empirical relations in long wavelength limit. Observed changes in linear optical parameters (increase in refractive index, and extinction coefficient; reduction in optical bandgap), nonlinear optical parameter (increase in χ(3)) are proposed for various photonic applications.