Study on the field distribution of the probes in scanning near-field optical microscope using finite-difference time-domain calculations

Scanning near-field optical microscope (SNOM) can provides optical imaging with ultrahigh resolution owing to its breakthrough the limit of optical diffraction, Metal coated optical fiber probe in nano-scale is one of the most important parts in aperture type of SNOM. Tip diameter and structure determine the final spatial resolution and experimental utility of SNOM. In order to understand the behavior of light propagation in the probes, we have investigated two kinds of three-dimensional probe models (metal coated and uncoated) by solving Maxwell equations with the Finite-Difference Time-Domain (FDTD) method. The three-dimensional (3D) computation reveals that the field distributions of light in the probes are some patterns due to the polarization of light and the structure of the probe. This result can guide to find optimized tip design.