Near resonant nanosecond laser driven nonlinear optical response in As50S50 thin films

TL;DR

This paper reports exceptionally strong nonlinear optical responses in As50S50 thin films under nanosecond near resonant excitation, revealing potential for optical limiting applications and explaining the effects with a five-level energy model.

Contribution

It introduces the strongest nonlinear optical response in amorphous semiconductors and proposes a five-level energy model to explain reverse saturable absorption and self-defocusing effects.

Findings

Nonlinear absorption coefficient up to 4 x 10^6 cm/GW

Nonlinear refractive index of 8.5 cm^2/GW

Effective application as an optical limiter

Abstract

Nanosecond near resonant excitation in As50S50 thin films leads to strong nonlinear optical response, i.e. nonlinear absorption coefficient up to 4 x 106 cm/GW and nonlinear refractive index of 8.5 cm2/GW, both of which is the strongest ever reported in amorphous semiconductors. We propose a five-level energy model to explain such effect which indicates that nonlinear process is reverse saturable absorption in nature, mediated by excited state absorption from triplet-triplet transition. On the other hand, observation of negative nonlinear refractive index reveals the occurrence of self-defocusing effect. Finally, benefitting from the strong nonlinear response, we demonstrate a promising application of As50S50 thin films as an optical limiter for optoelectronic sensors.