Preparation and third-order optical nonlinearity of gold nanoparticles incorporated mesoporous TiO₂ thin films

A kind of Au nanoparticle (NP) containing 2D hexagonal mesoporous TiO ₂ thin films (MTTFs) has been successfully synthesized through a deposition-precipitation method. The Au NPs show uniform size distribution and the An content within the MTTFs is measured to be 7.49 wt.%. The third-order nonlinear optical refractive index of the Au NPs contained MTTFs has been measured by the Z-scan technique at 1064 nm. The absolute value of nonlinear refractive index (n₂) and third-order nonlinear susceptibility (χ⁽³⁾) were calculated to be 2.64 × 10^-7 and 6.32 × 10^-8 esu, respectively. The high nonlinearity of the composite thin films can be attributed to the intraband transition of electrons near the Fermi surface in well-dispersed Au NPs confined in mesoporous channels and the high linear refractive index of the nanocrystalline anatase framework.