Investigation of some electromagnetic modes in the metal-dielectric system by the absorption spectrum

The surface plasmon resonance and the spherical cavity resonance in the system of a layer of periodically arranged dielectric spheres laid on outside of a metal slab or embedded in the metal substrate are investigated by observing the absorption spectrum. The absorption spectra for these systems can be accurately calculated by multiple scattering approaches. The calculated results show that there are some absorption peaks, which can be identified to the resonances of surface plasmon or cavity modes. The surface plasmon resonance occurs when the metal-dielectric interface is periodically modulated, as in both of the systems we considered. The frequency of the surface plasmon resonance is mainly determined by the periodicity of the modulated surface, and can be obtained by an analytic theory. Our calculated results are consistent very well with the analytic ones for both thick and thin metal slab. The cavity resonances only occur for the system of dielectric spheres embedded in a metal substrate. In this system, the resonances of both of the cavity mode and the surface plasmon coexist. In general, the absorption peaks for both of them are relatively weak, because their resonance frequency is far from each other. However, we can design the system to be that the resonances of the cavity mode and the surface plasmon are in almost the same frequency. In this case, a sympathetic resonance will occur, where the absorbance will be dramatically enhanced at the frequency.