Au/TiO2/SiO2 sandwich multilayer composite films with large nonlinear optical susceptibility

Au/TiO2/SiO2 sandwich composite multilayer films were deposited by alternating multitarget magnetron sputtering technique. Annealing process was performed for as-growth. Au particles appeared between the layers and grew with the increasing of the annealing temperature. The surface plasmon resonance of the annealed films is around 570-590 nm. The third-order nonlinear susceptibility was measured with the backward degenerate four wave mixing (DFWM) scheme at a 532 nm wavelength. The calculated values of χ(3) at 532 nm of the composite films are larger than 1.02 × 10−6 esu. We assume the multilayer sandwich topology of the Au/TiO2/SiO2 composite films has greatly enhanced the local field factor f and caused a larger χ(3) which is even not measured at the wavelength near the surface plasmon resonance of the composite materials.