Nonlinear absorption in media with composite gold nanoparticles

Abstract

We consider nonlinear absorption in a system consisting of a dilute mixture of identical metallic nanoparticles in a dielectric background. The nanoparticles consist of a core and a shell, one of which is gold and the other is a dielectric. By determining the effective nonlinear parameters of the nanoparticles, we find that the nonlinear absorption can be positive or negative, depending on the filling fraction of the gold. This shows that the magnitude and sign of the effective parameters depend not only on the constituent materials, but also on the details of the geometry.