Dispersions of two-photon and three-photon absorption in GaS films from 540 to 1600 nm

The development of nonlinear optical materials with strong multiphoton absorption (MPA) is crucial for the design of ultrafast nonlinear optical devices, such as optical limiters and all-optical switchers. In this study, we present the wavelengthdependent coefficients of two-photon absorption (2PA) and three-photon absorption (3PA) in a GaS film across a broad range of wavelengths from 540 to 1600 nm. The observed dispersions in the 2PA and 3PA coefficients align well with the widely used two-band approximation model applied to direct bandgap semiconductors. Notably, the GaS film exhibits exceptional MPA properties with a maximum 2PA coefficient of 19.89 cm/GW at 620 nm and a maximum 3PA coefficient of 4.88 cm3/GW2 at 1500 nm. The GaS film surpasses those found in traditional wide-bandgap semiconductors like beta-Ga2O3, GaN, ZnO, and ZnS while remaining comparable to monolayer MoS2, CsPbBr3, and (C4H9NH3)2PbBr4 perovskites. By employing a simplified two-energy-level model analysis, our results indicate that these large MPA coefficients are primarily determined by the remarkable absorption cross sections, which are approximately 4.82 x 10-52<middle dot>cm4<middle dot>s<middle dot>photon-1 at 620 nm for 2PA and 8.17 x 10-80<middle dot>cm6<middle dot>s2<middle dot>photon-2 at 1500 nm for 3PA. Our findings demonstrate significant potential for utilizing GaS films in nonlinear optical applications.