Measurements of the Third-Order Nonlinear Susceptibility of Ag Nanoparticles in glass matrices in a Wide Spectral Range

We determined the third-order susceptibility |χ(3)| of a thin composite film formed by silver nanoclusters embedded in soda-lime glass. Ag aggregation was promoted by irradiating an Ag-Na ion-exchanged glass with an N+ beam. |χ(3)| dispersion was measured by phase-mismatched degenerate four-wave mixing in the 380–470 nm spectral range, with 0.5 ps laser pulse duration. Close to the surface plasmon resonance of Ag metallic clusters, the χ(3) amplitude exceeds by a factor of 104 the value of substrate glass. We also measured a phase of 83° and a dynamics characterized by ~ 30, 3 and 0.9 ps decay times, ascribed to hot-electrons-lattice thermalization in the clusters, followed by thermal diffusion toward the matrix and relaxation of the whole system to the starting temperature.