DIRECT MEASUREMENT OF STANDING EVANESCENT WAVES WITH A PHOTON-SCANNING TUNNELING MICROSCOPE

We present a detailed analysis of a standing evanescent wave that is c aused by total internal reflection of an Ar-ion laser beam on a glass prism and investigate the coupling to a subwavelength dielectric tip o f a photon-scanning tunneling microscope that is raster scanned at a c lose distance over the prism surface. The intensity of the evanescent field is spatially modulated with a period of 239.2 nm. It decays expo nentially with a constant of 103.9 nm with increasing distance from th e prism surface. Precise measurements of the standing evanescent wave can be used to calibrate the scanner and permit one to determine the s patial resolution and the coupling efficiency of the tip.