Thermal nonlinear refraction properties of Ag2S semiconductor nanocrystals with its application as a low power optical limiter

In this work, nonlinear refraction properties of 3 nm sized silver sulfide (Ag2S) semiconductor nanocrystals dispersed in the dimethyl sulfoxide with varying concentrations are reported. Observation of the colloids far-field diffraction ring patterns indicates of large induced thermal nonlinear refraction in the medium. The thermally induced effective nonlinear refractive index due to nonlocal heat effect is characterized by Z-scan technique with a low power CW laser irradiation at 532 nm. This allows us to measure thermo-optic coefficient and effective nonlinear refractive index up to −1.52 × 10−7 cm2/W in the tested samples. Low power optical limiting, with low limiting thresholds is obtained in the samples based on thermal defocusing and self diffraction. The limiting thresholds of colloids at different Ag2S nanocrystals concentrations are also reported.

Research Highlights
► Ag2S nanoparticle fabrication by laser ablation of silver plate in DMSO.
► Large nonlinear refractive index measurements of the colloids.
► Promising nanoparticle material for a low power optical limiter.
► Achieving desirable limiting threshold by varying the nanoparticle concentration.