Sample–tip coupling efficiencies of the photon-scanning tunneling microscope

Abstract

The photon-scanning tunneling microscope is the photon analog to the electron-scanning tunneling microscope. It uses the evanescent field due to the total internal reflection of a light beam in a prism, modulated by a sample attached to the prism. The exponential decay of the evanescent field is characterized by the penetration depth dp and depends on the angle of incidence θ, the wavelength, and the polarization of the incident beam. The 1/e decay lengths range from 150 to 265 nm as deduced from the expression of the electric-field intensity in the rarer medium for θ = π/2. If we place another optically transparent medium near the surface, frustrated total reflection occurs. It is shown theoretically and experimentally that, if we choose an appropriate angle of incidence θ(θ ≠ π/2) and change the index of refraction of one of the media, the decay length of the electric field can be extremely small, so that images with an improved resolution can be produced.