Imaging of a sphere on a dielectric surface with scanning tunneling photon microscopy

Photon scanning tunneling microscopy has been used to image a dielectric interface (substrate index of refraction n>1) via an evanescent field present above the surface (in air, n'=1). In this work we consider the imaging of a sphere with arbitrary relative index of refraction n''>1 in the evanescent field. It is shown that the resolution is good for λ>a, where λ and a are the illuminating wavelength and radius, respectively. The observed intensity, which is the superposition of the propagating discrete modes excited in the sphere by the evanescent field, is calculated for various parameters. (orig.)