Resolution Analysis of a Polymethylmethacrylate Tapered Probe in Near-Field Terahertz Imaging

摘要

A Polymethylmethacrylate (PMMA) rectangular tapered probe with metal coating on the sides is analyzed as a near-field imaging probe at 100 GHz in Ansoft High Frequency Structure Simulator (HFSS). Normally, highly resistive silicon and sapphire, which are costly, are used as a near-field probe due to their low loss and high permittivity. PMMA near-field probe is usually used in Scanning Near-field Optical Microscopy (SNOM), which is made from PMMA optical fibers. We propose for the first time to use PMMA as a near-field probe in millimeter and Terahertz wave scanning near-field imaging applications. The geometrical optimization of the tapered probe is carried out on the basis of different coupling methods. The beam shape merging from the end of the tapered tip is analyzed. The operation efficiency of two-side tapered and four-side tapered probes has been compared in view of the fabrication technique. A knife edge is simulated in HFSS to define the lateral resolution. Longitudinal resolution is discussed through setting a stair step shaped sample. A high lateral resolution around the end of the probe size can be achieved and even higher longitudinal resolution. The impact of the tip-sample distance and the lateral resolution are clearly illustrated via simulations. Experiments are carried out using a two-side tapered probe provided with an aluminum coating. The resolution is defined by scanning a PMMA board which was half coated with aluminum.