Development of a Scanning Near-Field Sub-THz-Wave Microscopy with Coherent Transition Radiation

In order to establish the technique of near-field microscopy using an accelerator-based coherent radiation, some basic properties are experimentally investigated with coherent transition radiation (CTR) from a linac. In the transmission mode, the spatial resolution power in accepting whole wavelengths of CTR was 4.4, which was obtained by scanning the metallic plate edge with a metallic conical cone as an illumination probe. It was found that the probe with a dielectric film effectively scattered the near-field. The dependence of the resolution power with the wavelength was investigated with a conical cone of Teflon coated by silver paste on the tapered surface as an illumination probe. The resolution power became large with increasing the wavelength. In the reflection mode, two types of optical configuration were prepared to detect the reflected light, i.e. the beam-splitter type and the light-guide type. The spatial resolution powers in the two configurations were 4.4 and 4.6, respectively.