Superconducting detectors with high-speed and high-resolution at THz band.

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Using high Tc superconducting (HTS) grain boundary Josephson junctions (GBJJs) made of YBa_2Cu_3O_<7-x> (YBCO) deposited across bicrystal boundary, we have successfully demonstrated wide band detections at frequency as high as 2.5 THz and at operating temperature up to 70K.Also, up to 2.5 THz, the high-order harmonic mixing at zero and finite bias voltage have been demonstrated. The effect of applied dc magnetic field on the THz responses of GBJJs has been investigated in detail. The enhancement of the Shapiro step height could be obtained in the high-quality wider GBJJs when a dc field was applied. For this effect, simulation by an equivalent double-junction SQUID model is justified. It was found that the obtained restults agreed with the simulation results very well. So, the high-quality wider GBJJs with an external dc magnetic field may be more useful than the small GBJJs for detecting system at THz band. Also, it was found that the HTS planar antenna, which is useful to improve the coupling between the devices and THz signals, could be simply characterized at low temperature using HTS GBJJs. Furthermore, using the quasi-optical technology, the detecting system with a mind-refrigerator, which will minimize the whole system, has been designed and made-up. The THz responses have been measured when the HTS GBJJs was load in the small-sized refrigerator and it was found the formed system worked quite well. Finally, to make the measurements simply during a short time, a program with Hilbert transform and so on has been developed to collect and analyze tlue data. The results show that it is very hopeful using HTS GBJJs to form the detecting system with high-speed and high-resolution operating at the high temperature.