Femtosecond optical nonlinearities of Au/TiO2 thin films prepared by a sputtering method

A multitarget sputtering method was applied to embed Au nanoparticles in TiO2 thin films (Au/TiO2 films) with a high concentration of Au particles (19–41 at%). The absolute values of imaginary part of the third-order nonlinear susceptibility, |Im [χ(3)]|, of the Au/TiO2 films, exhibited a peak around the localized surface plasmon resonance absorption peak (around 660 nm), and the maximum value was estimated to be 3.6 × 10−7 esu measured by the femtosecond Z-scan technique. The figure of merit, |Im [χ(3)]|/α, (α is the absorption coefficient of the film at the corresponding wavelength of the measurement) of the film was calculated to be 1.4 × 10−12 esu·cm, which was larger than that of the Au/SiO2 film. This is mainly due to the local field enhancement.