Green's function approach to investigate the excitation of surface plasmon polaritons in a nanometer-thin metal film

Abstract

The two-dimensional magnetic-field Green's function for a nanometer-thin metal film embedded in a dielectric environment is constructed with the mode-expansion method. Explicit expressions are obtained for the Green's-function components related to the excitation of symmetric and antisymmetric surface-plasmon polariton (SPP) waves and out-of-plane propagating waves, respectively. The obtained expressions are used to study the power emitted by a magnetic dipole line source into the different radiation channels. For a wavelength of $\ensuremath{\lambda}=500$ nm the total emitted power is found to increase by a factor of three (the Purcell factor), with approximately 60% going into SPP waves when the source is placed directly on the surface of a 15-nm-thick silver film. Results obtained with and without including ohmic losses in the calculations are only negligibly different. The presented semianalytical approach allows for an exact analysis of the excitation of SPP waves on nanometer-thin metal films and may therefore find several applications within nanoplasmonics.