Development of high-frequency scanning near-field microscopy and investigation of its applications

Diffraction effects limit the resolution of conventional imaging microscopes to about the radiation wavelength used. However, sub-wavelength resolution below the diffraction limit can be achieved by the technique of scanning near-filed microscopy. The objective of this research project is to develop new microscopy formats and their related technologies in the millimeter-wave and terahertz regions in regard to our original microscope system using a metal slit-type probe that we had developed mainly in the millimeter-wave region, and to investigate new applications of the millimeter-wave and terahertz microscopy.We have proposed and experimentally demonstrated scanning near-field anisotropy microscopy in the millimeter-wave region, permitting the observation of electrical anisotropy in the viewed object. We also proposed a passive microscopy format that enables completely non-destructive and non-invasive measurements and succeeded to experimentally demonstrate its image reconstruction principle in the millimeter-wave region. In order to improve measurement sensitivity of the slit probe, we have proposed, designed and fabricated a resonant slit-type probe for millimeter-wave microscopy. Experiments performed in the millimeter-wave region show that the resonant probe has more than ten times greater sensitivity than a conventional tapered slit-type probe.To demonstrate terahertz microscopy using a slit-type probe, we have tried to optimize the geometry of the tapered slit probe operated at a terahertz frequency band of 0.3 THz. Based on the design criteria derived from the optimization process, a tapered slit probe was fabricated by electro-forming technique. We have verified that the measured RF performance of the probe agrees well with the predicted one obtained using the finite element method.We have applied the above mentioned microscopy formats and technologies to the characterization of planar dielectric substrates, liquid crystal materials etc. in the millimeter-wave region. Effectiveness of them has been experimentally verified.