We present third-order optical nonlinearities of Ag nanoparticles fabricated using a two-step ion exchange method. The
nonlinearities are studied using the well-known Z-scan technique. In our experiments, we use a Ti-Sapphire laser source
operating at 800 nm, which is far from the resonance of the Ag nanoparticles. The nonlinear refraction of these
nanoparticles is studied using the closed aperture configuration of the Z-scan method. Contrary to expectations from
previous studies for similar-sized nanoparticles, our nanoparticles possess positive nonlinear refractive index. The
estimated nonlinear refractive indices are in the range of 10-12 cm2/W.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.