Nonlinear optical behaviour in amorphous GeSeSb thin films

Abstract

In this paper we report nonlinear saturable absorption (SA) and other linear optical properties of amorphous chalcogenide- GeSeSb thin films. Chalcogenide glasses (chgs) are well known to possess large optical nonlinearity, high refractive index, wide infrared transparency etc. Here we have fabricated uniform thin films of different thickness from bulk GeSeSb glass via thermal evaporation method. Absorption and transmission measurements were done using UV–VIS-NIR spectrophotometer. A shift in absorption edge to higher wavelength with increase in film thickness has been observed. Linear refractive index was calculated by Swanepoel’s method and non linear studies were conducted by z-scan analysis. From this study we have found that these thin films are good saturable absorbers (SA). Our previous observations have confirmed that solution processed chalcogenide glasses shows reverse saturable absorption (RSA) properties, which increases with solute concentration. Collating both results we could infer that while moving from chalcogenide glass nanocolloids to chalcogenide glass thin films, these materials shows RSA to SA switching. High refractive index and high optical nonlinearity of chalcogenide glasses pave way for optical wave guides and logic gates applications.