Evaluation of the third-order optical nonlinearity of Au:SiO2 nanocomposites in the off-resonant spectral region

The third-order nonlinear optical susceptibility (χ(3)) of Au:SiO2 nanocomposite films with different Au particle sizes was measured to be on the order of 10−10 esu to 10−9 esu in the off-resonant spectral region, and the particle size-dependent behavior of χ(3) was observed. The results were found to deviate substantially from those of the conventional Maxwell-Garnet theory. By adapting the modified invariant imbedding method, which takes into account the effect of interparticle interactions on the nonlinear response, we successfully explain the enhanced third-order nonlinear susceptibility of metal–dielectric nanocomposites at off-resonant wavelengths.