Enhancement of optical nonlinearity in binary metal–nanoparticle arrays

Periodic binary metal–nanoparticle arrays, comprising of Au and Fe, were fabricated on quartz substrates using nanosphere lithography and pulsed laser deposition technique. The dimension of the obtained triangular Au(Fe) particles was about 80 nm which was defined by the single-layer masks prepared by self-assembly of polystyrene nanospheres with radius R = 100 nm. The structural characterization of the particle arrays was investigated by atomic force microscopy. In the optical absorption spectra, the metal–nanoparticle arrays show a strong absorption peak of ~ 550 nm due to the surface plasmon resonance of metal particles. The nonlinear optical properties of the nanoparticle arrays were determined using a single beam z-scan method at a wavelength of 532 nm with laser duration of 55 ps. By adding Fe, the resonant absorption of Au particles was quenched, and the figure of merit χ(3)/α (with χ(3) being the third-order nonlinear susceptibility, α being the absorption coefficient) was obviously increased. The obtained maximum χ(3)/α is about 6.15 × 10− 12 esu cm. The results show that periodic Au + Fe nanoparticle arrays exhibit a large nonlinear optical property with fast response.