Nanosecond high-order nonlinear optical effects in wide band gap silver sulfide nanoparticles colloids

In this paper, we report the magnitude and the sign of optical nonlinearities of silver sulphide nanoparticles (Ag2S NPs) dispersed in the dimethyl sulfoxide (DMSO) under exposure to 532 nm, 15 nanosecond (ns) pulsed laser irradiation. Large enhancement of two-photon absorption effect is observed with increase in concentration of the Ag2S NPs in the DMSO. The closed-aperture Z-scan data with ns pulsed laser shows a positive nonlinear refraction which is in agreement with the two-band model of Sheik-Bahae. This reveals that the bound electronic nonlinearity (third-order nonlinearity) is the dominant mechanism causing nonlinear refraction in the colloids. The presence of a fifth-order nonlinear refraction is also observed and analyzed. The concentration dependence of the optical liming is also investigated. The optical limiting threshold and the clamping energy decrease with increasing the Ag2S NPs in the DMSO. The nonlinear optical performance of the Ag2S NPs colloids in ns time regime in comparison with the reported continuous-wave (CW) nonlinear optical results is discussed. The results show that Ag2S NPs colloid could be a very promising medium for nonlinear photonics devices in both time regimes.