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.