Measurement of the third-order nonlinear susceptibility of Ag nanoparticles in glass in a wide spectral range

We determined the third-order susceptibility \X-(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. \X-(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 X-(3) amplitude exceeds by a factor of 10(4) the value of substrate glass. We also measured a phase of 83 degrees and a dynamics characterized by similar to 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.