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Near-Field Surface Plasmon Excitation on Structured Gold Films

Surface plasmon polariton (SPP) localization control on rough metal surfaces has been achieved by varying the gap between a scanning near-field aperture probe and the surface. The qualitative explanation for this observation is based on the overlapping of spatial frequencies available for near-field excitation of the SPP, with the spectral distribution of spatial frequencies characterizing the surface roughness. From a practical point of view, this selective excitation of electromagnetic states on nanostructures provides a way to estimate the reflectivity of structures such as grooves engraved into the metal film. Qualitative aspects of transmission and scattering through parallel slit pairs acting as Fabry-Perot resonators are discussed.