Coupling of surface-plasmon polaritons to directional far-field radiation by an individual surface protrusion

摘要

An experimental study of surface-plasmon polariton scattering by an individual surface protrusion on a silver film has been performed. Both in- and out-of-plane scattering have been investigated by imaging with a photon-scanning tunneling microscope at various probe-to-sample distances. For imaging in close proximity we observed a bright spot with rims on the shadow side, but, for imaging at larger distances, the location of the bright spot shifts away from the direction of the incoming surface-plasmon polariton. We estimate a pronounced peak in the far-field scattering pattern at an angle of ～20° from the sample plane, which is in good agreement with recent theoretical studies and indicates that the same protrusion could possibly be used for local launching of surface-plasmon polaritons in a reversed illumination configuration.