Third-order optical nonlinearity of gold nanoparticle arrays embedded in a BaTiO₃ matrix

Au:BaTiO₃ composite films comprising hexagon-shaped Au nanoparticle arrays covered with BaTiO₃ matrix were fabricated by double-layer nanosphere lithography and pulsed laser deposition technique. The optical nonlinearity of the composite film was determined using the Z-scan technique at a wavelength of 532 nm and a pulse duration of 25 ps. The third-order nonlinear optical susceptibility, χ⁽³⁾, was found to be 2.9 × 10"⁸ esu, which is comparable with the best values in metal-dielectric films comprising randomly distributed spherical particles but with much higher metal concentrations. The local electric field enhancement in and near the particles was investigated using the dipole discrete approximation method.