Enhanced optical nonlinear absorption of graded Au–TiO2 composite films

Abstract

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 βeff of single-layer Au-TiO2 films is measured to be −2.3 × 103 – 0.76 × 103 cm/GW with Au atom content 15%–66%. The βeff value of the 10-layer Au-TiO2 graded film is enhanced to be −2.1 × 104cm/GW calculated from p-polarized Z-scans, which is about ten times the maximum βeff 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.