Theory of surface-plasmon resonance optical-field enhancement at prolate spheroids

The optical-field enhancement from plasmon resonance at spheroids is studied by solving Maxwell equations using spheroidal vector wave functions. This treatment is an extension of the Mie theory for spheres. The phase retardation or dephasing effects, as studied by finite-element methods in a previous article, are confirmed. Nevertheless, the optical-field enhancement is shown to be substantial under certain resonance conditions. It is suggested that the positions of the resonances in parameter space are determined by global antenna properties and the magnitude of the field enhancement by local plasmon resonance.