Surface plasmon polariton scattering by finite-size nanoparticles

The electromagnetic Green's tensor approach (GTA) is used to obtain the differential and total scattering cross sections of a finite-size nanoparticle located at a metal surface and illuminated with surface plasmon polaritons (SPPs). The scattering process comprehends either elastic scattering of the incident SPP into other SPPs propagating in different directions or scattering into field components propagating away from the surface, as well as the radiation absorption by the (metal) nanoparticle. Once the total electric field inside the scatterer is known, the expressions obtained allow for a comparison of the efficiency of the different scattering channels. Connection between the GTA and the point-dipole approximation (PDA) of the scattering problem is discussed, including the absorption of the SPP and the transition from the GTA to the PDA when the scatterer is approximated by a spherical particle of the same volume. SPP extinction spectra for gold cubic particles of various sizes placed in the vicinity of a flat gold surface are calculated with the GTA and compared with the results obtained using the PDA.