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

摘要

Third-order optical nonlinearitis in three types of Au/dielectric composite thin films (Au/SiO_2,Au/Al-2O_3,and Au/TiO_2 films) with high concentrations (approx27 at.%) of Au 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 peakwas 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 susceptibiltiy,|Im[X~(3)]|/alpha,of the Au/SiO_2,Au/Al-2O_3,and Au/TiO_2 films increasd in that order,due to the local field enhancement.