Detection Of THz Signals Based On Superconducting HEB

Today all radiation detection systems in THz spectral region can be divided into heterodyne (coherent) detection and direct (incoherent) detection, which is based on the different types of detectors. However, except some thermal detectors with long response time, many detectors can be used not only as heterodyne but also direct detectors, and superconducting hot electron bolometer (HEB) is one of them. When temperature is around the superconductor critical temperature of HEB, the tiny change of temperature can cause the large variation of HEB’s impedance, which can reflect the amplitude of THz radiation and is the basis of HEB working as a direct detector.In this thesis, we describe a novel method of terahertz direct detection, which is based on a superconducting NbN HEB chip operated under the influence of a microwave pump. In our detection system, the chip is driven by a microwave source which can be adjusted easily. By pumping in appropriate microwave signal (with frequency～1.5 GHz and power～-16.52 dBm) and DC bias (with 0.25 mV bias voltage and 12 μA bias current) to the chip, its best bias working point is achieved to detect THz radiation directly. The measured best noise equivalent power is 8×10-12 W/(?)Hz and the system response shows a good linear relationship with the incident power of radiation.Besides, we build a fast THz direct detection system by combining this superconducting NbN HEB direct director and a Fourier transform spectrometer (FTS) constructed by ourselves in laboratory. With this system, we measured the frequency characterization of metal mesh filter and the radiation spectrum of quantum cascaded laser (QCL) operated in pulse mode. At the same time, the measurement results are compared with those achieved by using commercial Golay Cell and cryogenic semiconductor bolometer, and the final results show that the superconducting NbN HEB direct detection system built by us can perform better than Golay Cell, and perform well with the commercial cryogenic silicon bolometer, in addition, its response speed is far faster than these two detectors.