The third-order optical nonlinearity of Fe2O3 nanoparticles capped with glutamic acid molecules and bare particles in hydrosol have been investigated by Z-scan technique. The signs and magnitudes of nonlinear refractive coefficients (γ) of these two kinds Fe2O3 nanoparticles were obtained. The results suggested that γ was intensively subject to the surface-capping molecules. This phenomenon may be in particular considered with local field enhancement effect related to the refractive index of the media around nanoparticles, and the local field enhancement factor was evaluated by the solution of Laplace's equation.
The extinction spectra as well as Hyper-Rayleigh scattering (HRS) signals from three volume silver nanoparticles with aggregate effect have been measured. The morphology of silver aggregates is observed as chain-like aggregate by TEM. Strong enhancements of HRS signals are found when aggregation occurs, and reversed enhancement factor versus particle size is found. The observed size dependence of the second harmonic generation from silver nanoparticle with aggregates effect is explained by assuming surface contribution. Analysis on the extinction spectra and the HRS responses suggests two mechanisms may participate the surface contribution. The first one is arising from the breaking of centrosymmetry at the particles' surface. Another one is the enhanced electromagnetic (EM) field near the particles' surface.