Multilayer Au/TiO₂Composite Films with Ultrafast Third-Order Nonlinear Optical Properties

We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO₂ composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590nm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser (50fs) at the wavelength of 800nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66×10^-10m/W and -2.95×10^-17m²/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.