Enhancement of nonlinear optical properties of Au–TiO 2 granular composite with high percolation threshold

Two series of Au–TiO 2 composite films with Au percola‐ tion threshold q C 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 q C increases from 0.34 to 0.82, the plasmon resonant absorption of the composite films near q C 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 × 10 4 cm/GW to 1.7 × 10 5 cm/GW, and the maximal nonlinear refraction index increases from a very small value to –2.6 cm 2 /GW. The large second‐ and third‐order optical nonlinearity of the Au–TiO 2 composite films with high q C 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)