Optical properties of a plasmonic nano-antenna: an analytical approach

The optical properties of a plasmonic nano-antenna made of two metallic nanospheroids (prolate or oblate) were investigated analytically in quasi-static approximation. It is shown that in clusters of two nanospheroids, three types of plasmonic modes can be present. Two of them can be effectively excited by a plane electromagnetic wave, while the third one can be effectively excited only by a nanolocalized light source (an atom, a molecule or a quantum dot) placed in the gap between the nanoparticles. Analytical expressions for the absorption cross-section, the enhancement of local fields and the radiative decay rate of an excited atom placed near such a nano-antenna are presented and analyzed.