Size Dependent χ(3) for Conduction Electrons in Ag Nanoparticles

Our theoretical study of the third-order susceptibility (χ(3)) for Ag dielectric composite reveals a critical role of saturation of optical transitions between discrete states of conduction electrons in metal quantum dots. The calculated size dependence of the χ(3) for Ag nanoparticles reproduces the published experimental results. Saturation effects lead to a decrease of the local field enhancement factor that is of particular importance for surface-enhanced phenomena, such as Raman scattering and nonlinear optical responses.