Enhanced optical nonlinear absorption of graded Au-TiO2 composite films

This paper reports that single-layer and graded Au TiO2 granular composite films with Au atom content 15%-66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized Z-scans in femtosecond time scale. The nonlinear absorption coefficient beta(eff) of single-layer Au-TiO2 films is measured to be -2.3x10(3)-0.76x10(3) cm/GW with Au atom content 15%-66%. The beta(eff) value of the 10-layer Au TiO2 graded film is enhanced to be -2.1 x 10(4)cm/gw calculated from p-polarized Z-scans, which is about ten times the maximum beta(eff) of single-layer films. Broadened response in the wavelength region 730-860 nm of the enhanced optical nonlinearity of graded Au-TiO2 composite films was also investigated.