The Numerical Simulation Of The Scanning Imaging Of PSTM Probe With The Dispersive Medium

Scanning Near-field Optical Microscope (SNOM) is a near-field optical microscope that can measure local optical properties with high resolution beyond the diffraction limit, It can detect the sample harmless, study the biology alive, and even the translucent materials. So it is applied widely in lots of fields such as studies in biology and medicine in recent years.Photon Scanning Tunneling Microscope (PSTM) is one kind of SNOM, in the model of which, the surface evanescent wave, which is generated under total internal reflection condition, excites the sample to form a scattering field, then the near-field is detected by the optical fiber probe tip, in which it is transformed to propagating wave.The whole process refers to the scattering fields of the sample and fiber probe and the interaction between them, which make the analyses of the process more complicate. So, it is necessary to simulate the process numerically. In all kinds of the simulation methods, the Finite-Difference Time-Domain (FDTD) method is a simple and effective simulate algorithm which applied in the numerical simulation of the scanning near-field optical microscope (SNOM). But it is hardly applied in the study about the different types of the PSTM metallic fiber probe imaging.Based on former study, in the collection mode, the optical resolution is mainly determined by the shape of the probe. In this paper, considering the interaction of the probe and sample, we test the Pointing Vector distribution in a section at a certain height from the probe tip with equivalent incident wave method of the three dimensional FDTD and study the different imaging conditions of the four types of probes: bare fiber probe, metal coated aperture fiber probe, total metal-coated fiber probe, the one with metal particle on the tip and the metal-coated probe with a nanometric metallic pyramid in the tip. Furthermore, the influences of the parameters' changes in each kind of probe tip on the imaging are investigated and compared. These results we get are valuable for the selection of the probe parameters of the PSTM.