Large optical Kerr effect in matrix-embedded metal nanoparticles

We report an experimental and theoretical study on the third-order nonlinear optical properties of gold particles embedded in a dielectric host. Thin films of various metal concentrations are elaborated by the sputtering technique. Several complementary techniques provide information about the metal concentration, the film thickness and the size of the particles. The effective complex optical index of the film is determined by spectrophotometry and ellipsometry. The third-order nonlinear susceptibility, χ(3), is measured using the z-scan technique in the nanosecond regime. Experimental results reveal very large nonlinearities, increasing with the metal concentration. Theoretical calculations of the amplification factor, based on a recursive transfer method, allow a better understanding of these results.