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Semenov A, Richter H, Smirnov A, Günther B, Hübers H-W, Il’in K, et al. Development of HEB mixers for GREAT and for security screening [abstract]. In: Proc. 18th Int. Symp. Space Terahertz Technol.; 2007. 184.
Abstract: We report the study on the quasioptical coupling efficiency and the gain bandwidth of NbN hot-electron bolometer mixers developed for the 4.7 THz channel of the German receiver for Astronomy at THz-frequencies (GREAT) and for security screening at subterahertz frequencies. Radiation coupling efficiency and directive properties of integrated lens antennas with log-spiral, log-periodic and double-slot planar feeds coupled to a hot-electron bolometer were experimentally studied at frequencies from 1 THz to 6 THz and compared with simulations based on the method of moments and the physical-optics ray tracing. For all studied antennas the modeled spectral dependence of the coupling efficiency fits to the experimental data obtained with both Fourier transform spectroscopy and noise temperature measurements only if the complex impedance of the bolometer is explicitly taken into account. Our experimental data did not indicate any noticeable contribution of the quantum noise to the system noise temperature. The experimentally observed deviation of the beam pattern from the model prediction increases with frequency and is most likely due to a non- ideality of the presently used lenses. Study of the intermediate frequency mixer gain at local oscillator (LO) frequencies between 2.5 THz and 0.3 THz showed an increase of the gain bandwidth at low LO frequencies that was understood as the contribution of the direct interaction of magnetic vortices with the radiation field. We have found that the non- homogeneous hot-spot model more adequately describes variation of the intermediate frequency bandwidth with the applied local oscillator power than any of uniform mixer models. The state-of-the-day performance of the GREAT 4.7-THz channel and the 0.8-THz security scanner will be presented.
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Gol’tsman GN. The “Millimetron” project, a future space telescope mission [abstract]. In: Proc. 18th Int. Symp. Space Terahertz Technol.; 2007. 255.
Abstract: The goal of the Millimetron project is to develop a space observatory operating in the millimeter, sub-millimeter and infrared wavelength ranges using a 12-m actively cooled telescope in a single-dish mode and as an interferometer with the space-ground and space-space baselines (the later after the launch of the second identical space telescope). The Millimetron’s main reflector and other optics will be cooled down to 4K thus enabling astronomical observations with super high sensitivity in MM and subMM (down to nanoJansky level). Heterodyne observations in an interferometer mode at frequencies 0.1-1 THz will provide super high angular resolution. The main instruments, planned to be installed are wide-range imaging arrays, radiometers with spectrometers and polarimeters, VLBI heterodyne receivers, and Mikelson type interferometer devices. Wide-range MM and subMM imaging arrays and spectrometers will be based on a superconducting hot electron direct detectors with Andreev mirrors operating at 0.1 K. Such detectors are the best candidates to reach the noise equivalent power level of 10 -19 -10 -20 W/√Hz. Heterodyne receivers will be both SIS based superconducting integrated receiver with flux-flow oscillator as LO (0.1-0.9 THz range) and HEB based receivers using multiplied Gunn oscillator as LO for 1-2 THz range and quantum cascade lasers as LO for 2-5 THz range. For observations in middle IR region there will be installed large arrays of superconducting single photon detectors, providing imaging with very high dynamic range and ultimate sensitivity.
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Cherednichenko S, Khosropanah P, Berg T, Merkel H, Kollberg E, Drakinskiy V, et al. Optimization of HEB mixer for the Herschel Space Observatory [abstract]. In: Proc. 15th Int. Symp. Space Terahertz Technol.; 2004. 16.
Abstract: A mixer development for the HIFI instrument of the Herschel Space Observatory has come to the final stage. In our paper and conference presentation we will describe the most important details of the Band 6 Low and High Mixer Unit design. Special attention will be given to the optimization of the hot- electron bolometer mixer chip, which is based on 3.5nm NbN superconducting film on silicon. As the HEB’s local oscillator power requirements depend on the bolometer size, we have compared mixer noise temperature for different bolometer width- to- length ratio. A trade- off between mixer performance and local oscillator power requirements results in the mixer units equipped with optimized mixer chips, providing the largest coverage of the Band6 RF band with the lowest possible receiver noise. A short account of the beam pattern measurements of Band6 mixers will be given as well.
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Korneev A, Semenov A, Vodolazov D, Gol’tsman GN, Sobolewski R. Physics and operation of superconducting single-photon devices. In: Wördenweber R, Moshchalkov V, Bending S, Tafuri F, editors. Superconductors at the Nanoscale. De Gruyter; 2017. p. 279–308.
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Baselmans J, Kooi J, Baryshev A, Yang ZQ, Hajenius M, Gao JR, et al. Full characterization of small volume NbN HEB mixers for space applications. In: Proc. 16th Int. Symp. Space Terahertz Technol. Göteborg, Sweden; 2005. p. 457–62.
Abstract: NbN phonon cooled HEB’s are one of the most promising bolometer mixer technologies for (near) future (space) applications. Their performance is usually quantified by mea- suring the receiver noise temperature at a given IF frequency, usually around 1 – 2 GHz. However, for any real applications it is vital that one fully knows all the relevant properties of the mixer, including LO power, stability, direct detection, gain bandwidth and noise bandwidth, not only the noise temperature at low IF frequencies. To this aim we have measured all these parameters at the optimal operating point of one single, small volume quasioptical NbN HEB mixer. We find a minimum noise temperature of 900 K at 1.46 THz. We observe a direct detection effect indicated by a change in bias current when changing from a 300 K hot load to a 77 K cold load. Due to this effect we overestimate the noise temperature by about 22% using a 300 K hot load and a 77 K cold load. The LO power needed to reach the optimal operating point is 80 nW at the receiver lens front, 59 nW inside the NbN bridge. However, using the isothermal technique we find a power absorbed in the NbN bridge of 25 nW, a difference of about a factor 2. We obtain a gain bandwidth of 2.3 GHz and a noise bandwidth of 4 GHz. The system Allan time is about 1 sec. in a 50 MHz spectral bandwidth and a deviation from white noise integration (governed by the radiometer equation) occurs at 0.2 sec., which implies a maximum integration time of a few seconds in a 1 MHz bandwidth spectrometer.
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