Surface plasmon polariton propagation across a gentle silver step

Abstract Surface plasmon polaritons (SPPs) are excited with light of wavelength λ1=632.8 nm on or near a gentle Ag/Ag step structure using focused beam, prism coupling and detected using a bare, sharpened fibre tip. The tip–sample separation is controlled by means of an evanescent optical field at wavelength λ2=543.5 nm in a photon scanning tunnelling microscope (PSTM). The SPP propagation properties are first characterised on both the thin and thick sections of the Ag film structure either side of the step, both macroscopically, using attenuated total reflection, and microscopically from the PSTM images; the two techniques yield very good agreement. It is found that the SPP propagation len…