OICC Press Journal of Theoretical and Applied Physics 2251-7235 16 3 2023 11 17 Study of nonlinear optical properties of platinum and gold nanoparticles under a CW laser irradiation at 532 nm 10.30495/JTAP.162231 EN Mina Eslamifar Physics Department, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran 0000-0002-1770-8000 Journal Article 2023 11 17 This work presents a study on the thermo-optical properties of colloidal gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs) under a low power laser irradiation at 532 nm. Samples of gold and platinum are synthesized by nanosecond pulsed laser ablation of pure gold and platinum plates in the distilled water. The formation of the AuNPs and PtNPs has been evidenced by optical absorption spectra and transmission electron microscopy. The thermo-optical properties of AuNPs and PtNPs are studied using Z-scan technique. The nonlinear optical measurments exhibit a very large nonlinear refraction close to the surface plasmon resonance frequency of the nanoparticles. Our results reveal that the diffusion in the colloids is due to nonlocal thermal process. This work suggests that thermal nonlinear refraction will play an important role in development of photonic application involving metal nanoparticles colloids