In this paper, three types of simulations will be performed using the three-dimensional finite difference time domain (3D-FDTD) method. First, we simulate the visualized interaction procedure of evanescent field coupling to the PSTM probe tip. Then, we show the variation in the field distribution above the sample as its refractive index and thickness are increased. Finally, we simulate the refractive index images based on the principle of separation of the refractive index image from the images of AF/PSTM for the realistic experiments. The numerical results are in good coincidence with the experimental results.
It is important to analyze the images obtained by photon scanning tunneling microscope (PSTM). Recently some theories have been developed including finite-difference time-domain (FDTD) method applied in near field optics. In this article wc extend a simple FDTD method (equivalent incident wave method) to PSTM system, which has been widely used to detect objects buried underground in geophysics. In PSTM system lighting wave is evanescent wave, that is the equivalent incident wave exciting the samples and probe over the interface. Numerical simulations show that the results ofthis method are in agreement with the results ofthe moment method and perturbation theory.