Effect of dielectric matrices on femtosecond nonlinear optical properties of Au/dielectric composite thin films

Third-order optical nonlinearities in three types of Au/dielectric composite thin films (Au/SiO2, Au/Al2O3, and Au/TiO2 films) with high concentrations (similar to27 at.%) of An particles (5.6-16.8 nm in diameter) have been investigated by means of Z-scan and pump-probe techniques in the femtosecond time region. In the optical-absorption spectra of the films, the absorption peak of the surface plasmon resonance (SPR) of Au particles was clearly observed. The peak was shifted toward a longer wavelength with increasing the refractive index of the dielectric matrices. Near the SPR peak, the imaginary part of the third-order nonlinear susceptibility, \Im[chi((3))]\ / alpha, of the Au/Sio(2), Au/Al2O3, and Au/TiO2 films increased in that order, due to the local field enhancement.