Abstract: To put space-based and airborne heterodyne instruments into operation at frequencies above 1 THz the superconducting NbN hot-electron bolometer (HEB) will be incorporated into heterodyne receiver as a mixer. At frequencies above 1.3 THz the sensitivity of the NbN HEB mixers outperform the one of the Schottky diodes and SIS-mixers, and the receiver noise temperature of the NbN HEB mixers increase with frequency. In this paper we present the results of the noise temperature measurements within one batch of NbN HEB mixers based on 3.5 mn thick superconducting NbN film grown on Si substrate with MgO buffer layer at the LO frequencies 2.5 THz and 3.8 THz.

Abstract: The development of terahertz imaging instruments for security systems is on the cutting edge of terahertz technology. We are developing a THz imaging system based on a superconducting integrated receiver (SIR). An SIR is a new type of heterodyne receiver based on an SIS mixer integrated with a flux-flow oscillator (FFO) and a harmonic mixer which is used for phase-locking the FFO. Employing an SIR in an imaging system means building an entirely new instrument with many advantages compared to traditional systems.
In this project we propose a prototype THz imaging system using an 1 pixel SIR and 2D scanner. At a local oscillator frequency of 500 GHz the best noise equivalent temperature difference (NETD) of the SIR is 10 mK at an integration time of 1 s and a detection bandwidth of 4 GHz. The scanner consists of two rotating flat mirrors placed in front of the antenna consisting of a spherical primary reflector and an aspherical secondary reflector. The diameter of the primary reflector is 0.3 m. The operating frequency of the imaging system is 600 GHz, the frame rate is 0.1 FPS, the scanning area is 0.5 × 0.5 m2, the image resolution is 50 × 50 pixels, the distance from an object to the scanner was 3 m. We have obtained THz images with a spatial resolution of 8 mm and a NETD of less than 2 K.

Abstract: The research by the group of Moscow State Pedagogical University into the hot-electron phenomena in thin superconducting films has led to the development of new types of detectors and their use both in fundamental and applied studies. In this paper, we present the results of testing the terahertz HEB receiver systems based on ultrathin (∼ 4 nm) NbN and MoRe detectors with a response time of 50 ps and 1 ns, respectively. We have developed three types of devices which differ in the way a terahertz signal is coupled to the detector and cover the following ranges: 0.3–3 THz, 0.1–30 THz and 25–70 THz. In the case of the receiving system optimized for 0.3–3 THz, the sensitive element (a strip of asuperconductor with planar dimensions of 0.2μm (length) by 1.7μm (width)) was integrated witha planar broadband log-spiral antenna. For additional focusing ofthe incident radiation a silicon hyperhemispherical lens was used. For the 0.1–30 THz receivingsystem, the sensitive element was patterned as parallel strips(2μm wide each) filling an area of 500×500μm2with a filling factor of 0.5. In the receivingsystem of this type we used direct coupling of the incident radiation to the sensitive element. Inthe 25–70 THz range (detector type 2/2a in Table 1) we used a square-shaped superconductingdetector with planar dimensions of 10×10μm2. Incident radiation was coupled to the detectorwith the use of a germanium hyperhemispherical lens.The response time of the above receiving systems is determined by the cooling rate of the hotelectrons in the film. That depends on the electron-phonon interaction time, which is less forultrathin NbN than in MoRe.