Large third-order optical nonlinearity in Au:dielectric composite films in femtosecond time scale

Abstract

The large third-order nonlinear susceptibility, χ⁽³⁾, from Au:dielectric (SiO₂ and TiO₂) composite films near the Au percolation threshold is reported. The composite films were prepared by co-sputtering onto a fused silica substrate with varying Au composition. The wavelength dependence of the χ⁽³⁾ in an Au:SiO₂ composite film with 30% Au was measured by a degenerate four-wave mixing. In addition, χ⁽³⁾ was influenced by the Au concentration and matrix used. The enhancement mechanisms of the χ⁽³⁾ was divided into three parts: the first one has an instantaneous response, which stems from the interband electric-dipole transitions; the second one, is the hot electron contribution; and the last one is the thermal contribution with a very slow response time.