THRESHOLD-TUNABLE OPTICAL LIMITERS OF Au NANOPARTICLES IN CASTOR OIL

Optical limiting performance of gold nanoparticles (AuNPs) in castor oil is studied using a low power laser irradiation at 532 nm. Our results suggest that it is possible to tune the optical limiting threshold of the AuNPs by modifying the parameters of the set-up and gold nanoparticle concentration of the colloids. The closed Z-scan measurements reveal that non-local thermal nonlinear refraction process is responsible for the limiting action of the colloids. We have investigated the Z-scan behavior of the samples based on the non-local thermal nonlinear refraction process without using photo-thermal thin lens approximation. It is shown that this model is in good agreement with the experimental results and large enhancement factors are measured for values of nonlinear thermal refractive index and thermo-optical coefficients of the colloids at higher gold nanoparticle concentration compared to the measurement of castor oil.