Radiation Damping of Surface Plasmons in a Pair of Nanoparticles and in Nanoparticles near Interfaces

A theory of surface plasmon radiation damping in a system of coupled spherical metallic nanoparticles is developed, and a simple formula for the radiation line width is obtained for the first time. It is shown that as a result of surface plasmon frequency redshift, a notable reduction of the radiation damping rate takes place. For small separations, the radiation line width narrows by a factor of 3 as compared to large separations. The theory is expanded to the case of a spherical metallic nanoparticle placed near an interface of two dielectric media. The dependence of the redshift of surface plasmon frequency and the radiation damping rate on the particle–interface separation are calculated. It is revealed that in both cases, a decrease of refractive index of the surrounding media also leads to a decrease of the damping rate