Determination of the spatial extension of the surface-plasmon evanescent field of a silver film with a photon scanning tunneling microscope

Abstract

A photon scanning tunneling microscope is employed to probe the surface-plasmon field in the evanescent region of a silver film for p (parallel to the plane of incidence) and s (perpendicular to the plane of incidence) polarizations of the light beam at several angles of incidence near the critical angle. The interaction between the field and the probe is measured and compared to theoretical calculations involving a single four-media model. A systematic analysis of images obtained for several positions of the optical fiber above the film is presented and it is shown that, for tip-to-sample distances smaller than half the wavelength of the incoming light, the collected intensity curves are identical in any area of the sample.