Fast nonlinear refractive index of pure and alloy metallic nanoparticles in silica glass

Fast nonlinear refractive index and nonlinear absorption coefficient were measured at 527 nm of wavelength for composites formed by either copper or gold-silver alloy nanoparticles embedded in silica by the Z-scan technique. A single 6 ps long pulse from a Nd:glass laser was used in the Z-scan measurement, allowing to determine the fast (i.e., non-thermal) component of the nonlinear response. Both the composites exhibit relatively large (and negative for the Au-Ag alloy) nonlinear index. Transmission electron microscopy, optical absorption and extended X-ray absorption fine structure spectroscopies were also used to characterize the samples. Some figures of merit for the two samples were evaluated, as well as the third-order optical susceptibilities.