Analysis of image formation with a photon scanning tunneling microscope

The photon scanning tunneling microscope (PSTM) is based on the frustration of a total internal reflected beam by the end of an optical fiber. Until now it has been used to obtain topographic information, generally for smooth samples. We report theoretical as well as experimental results on the observation of a step on a quartz substrate with the PSTM. These results demonstrate the effects on image formation of the distance between the fiber tip and the sample surface, the orientation of the incident beam with respect to the step, the polarization, and the coherence of the light. Good agreement exists between numerical simulations and experiments. We show that a perturbative approach, whose validity has been checked by comparison with a rigorous volume integral method, provides physical insight into the main features of the different images. (C) 1996 Optical Society of America.