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Spirulina-templated metal μ coils (STMμC) are interesting materials for a wide range of terahertz (THz) applications due to their distinctive interactions with THz-light. We measured inclusive Mueller matrices of randomly distributed and one-dimensional (1D) STMμC-embedded paraffin sheets using Stokes polarimetry at 1.6 THz, where strong optical activity has already been reported. We demonstrated that the one-dimensional STMμC paraffin sheet can simultaneously express five polarization effects including linear-birefringence, linear-dichroism, circular-birefringence, circular-dichroism, and depolarization. Hence, STMμC can potentially be utilized for the control of various polarization phenomena of THz-light.

We designed, fabricated, and characterized a superconducting detector array for terahertz imaging applications. To evaluate the optical performance as an imaging array, we measured the spectral response of a 5-pixel linear array detector, and confirmed its sensitivity peaks to be at the same frequency within accuracy of one percent in the range of 0.65 THz. The frequency peaks are also in good agreement with a numerical calculation. This linear array was tested in the nondestructive imaging of a metallic pattern and an integrated-circuit card, and allowed the shortening of the total acquisition time. High fabrication yield of about 99% was achieved for single superconducting tunnel junctions, which led to 90% yield for the detectors.

Niobium-based superconducting tunnel junctions (STJs) with aluminum trapping layers as X-ray detectors were fabricated. We applied a fabrication technique for reducing the leakage current and improving the energy resolution for X-rays at around 6 keV. The edges of two Al layers sandwiching a tunneling barrier were oxidized by plasma discharge. The performance of these new STJs was compared with other types of STJs to which thermal oxidization in an O2 atmosphere had been applied. The oxidization process in O2 plasma significantly improved the energy resolution for X-rays, which reached values (FWHM) of 41 eV, 58 eV, 65 eV, and 129 eV for STJs with the size of 20×20 µm2, 100×100 µm2, 200×200 µm2, and 500×500 µm2, respectively.

Superconducting tunnel junctions exhibit excellent performance in energy resolution together with the high rate counting capabilities which cannot be realized with conventional radiation detectors. We discuss possible improvements in astronomy and other research fields by employing superconducting tunnel junctions as detectors of X-rays and visible photons.