Z-Scan Measurement in Amorphous As2S3 Thin Film

Z-scan technique is very useful method for measuring the magnitude and the sign of the nonlinear refractive index due to its simple geometry and high sensitivity compared with nonlinear interferometry, degenerate four-wave mixing, nearly degenerate three-wave mixing, ellipse rotation, beam distortion measurement.[1, 2] With this technique the measurements and analysis for several nonlinear optical materials such as CS2, ZnSe, GaAs, CdTe had been succesfully acomplished by using high power pulse laser.[1-3] In this paper, we present a cw pump-probe z-scan method for determining the optical nonlinearity of an amorphous As2S3 thin film. In an amorphous chalcogenide As2S3, thin film the optical nonlinearity originates from the photostructural changes of the material by band gap illumination (bandgap energy of Eg ≃ 2.5eV corresponding to Ar-ion laser wavelength of 514nm), which results in photodarkening and photoanisotropy. These effects have been extensively investigated as holographic recording medium for optical information processing, polarization hologram and binary phase gratings such as Dammann grating.[4-6]