Enhancement of nonlinear optical properties of Au–TiO2 granular composite with high percolation threshold

Abstract

AbstractTwo series of Au–TiO2 composite films with Au percola‐ tion threshold qC of 0.34 and 0.82 were prepared by using sputtering technique at the pressure of 5.0 × 10–2 and 8.0 × 10–2 Torr, respectively. As qC increases from 0.34 to 0.82, the plasmon resonant absorption of the composite films near qC shifts from about 700 nm to 760 nm, and the maximal second harmonic generation (SHG) intensity increases by 20%, the maximal nonlinear absorption coefficient increases from –3.0 × 104 cm/GW to 1.7 × 105 cm/GW, and the maximal nonlinear refraction index increases from a very small value to –2.6 cm2/GW. The large second‐ and third‐order optical nonlinearity of the Au–TiO2 composite films with high qC is attributed to the high density of Au particle in the nonconductive film and the strong local field enhancement caused by the surface plasmon resonant absorption. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)