Z-scan nonlinear optical properties of the Au-SiO 2 nanocomposite thin film

Au-SiO 2 nanocomposite thin film is fabricated reproducibly by co-sputtering method with the size of Au nano particles around 2 to 10 nm. TEM images display the irregular shape Au nanoparticles are embedded in SiO 2 thin film with random distribution. A surface plasmon absorption peak of Au nanoparticles is found in absorption spectra. The nonlinear optical properties are measured by confocal Z-scan method with a sub-nanosecond pulse laser (λ=532nm, pulse width 0.71ns, repetition rate 15.79kHz) and high-numerical-aperture objective lens (NA=0.55). Results of the Z-scan show nonlinear optical properties and enhanced transmittance at the focusing position of nanocomposite Au-SiO 2 films. The transmittance can be more than 135% for a 15-nm-thick Au-SiO 2 nanocomposite thin film with an average grain size of around 5 nm.