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Richter, H., Semenov, A., Hubers, H. - W., Smirnov, K., Gol’tsman, G., & Voronov, B. (2004). Phonon cooled hot-electron bolometric mixer for 1-5 THz. In Proc. 29th IRMMW / 12th THz (pp. 241–242).
Abstract: Heterodyne receivers for applications in astronomy and planetary research need quantum limited sensitivity. In instruments which are currently built for SOFIA and Herschel, superconducting hot electron bolometers (HEB) are used to achieve this goal at frequencies above 1.4 THz. In order to optimize the performance for this frequency of hot electron bolometer mixers with different in-plane dimensions and logarithmic-spiral feed antennas have been investigated. Their noise temperatures and beam patterns were measured. Above 3 THz the best performance was achieved with a superconducting bridge of 2.0/spl times/0.2 /spl mu/m/sup 2/ incorporated in a logarithmic spiral antenna. The DSB noise temperatures were 2700 K, 4700 and 6400 K at 3.1 THz, 4.3 THz and 5.2 THz, respectively. The results demonstrate that the NbN HEB is very well suited as a mixer for THz heterodyne receivers up to at least 5 THz.
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Hübers, H. - W., Semenov, A., Richter, H., Smirnov, K., Gol'tsman, G., & Voronov, B. (2002). Phonon cooled far-infrared hot electron bolometer mixer. In NASA/ADS.
Abstract: Heterodyne receivers for applications in astronomy need quantum-limited sensitivity. At frequencies above 1.4 THz superconducting hot electron bolometers (HEB) can be used to achieve this goal. We present results of the development of a quasi-optical phonon-cooled NbN HEB mixer for GREAT, the German heterodyne receiver for SOFIA. Different mixers with logarithmic spiral and double slot feed antennas have been investigated with respect to their noise temperature, conversion loss, linearity and beam pattern at several frequencies between 0.7 THz and 5.2 THz. At 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 16 dB. The response of the mixer was linear up to 400 K load temperature. This performance was verified by measuring an emission line of methanol at 2.5 THz. The results demonstrate that the NbN HEB is very well suited as a mixer for FIR heterodyne receivers.
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Semenov, A. D., Hübers, H. - W., Gol’tsman, G. N., & Smirnov, K. (2002). Superconducting quantum detector for astronomy and X-ray spectroscopy. In J. Pekola, B. Ruggiero, & P. Silvestrini (Eds.), Proc. Int. Workshop on Supercond. Nano-Electronics Devices (pp. 201–210). Boston, MA: Springer.
Abstract: We propose the novel concept of ultra-sensitive energy-dispersive superconducting quantum detectors prospective for applications in astronomy and X-ray spectroscopy. Depending on the superconducting material and operation conditions, such detector may allow realizing background limited noise equivalent power 10−21 W Hz−1/2 in the terahertz range when exposed to 4-K background radiation or counting of 6-keV photon with almost 10—4 energy resolution. Planar layout and relatively simple technology favor integration of elementary detectors into a detector array.
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Semenov, A., Hübers, H. - W., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2002). Performance of terahertz heterodyne receiver with a superconducting hot-electron mixer. In Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 229–234).
Abstract: During the past decade major advances have been made regarding low noise mixers for terahertz heterodyne receivers. State of the art hot-electron-bolometer (HEB) mixers have noise temperatures close to the quantum limit and require less than a microwatt power from the local oscillator (L0). The technology is now at a point where the performance of a practical receiver employing such mixer, rather than the figures of merit of the mixer itself, is of major concern. We have incorporated a phonon-cooled NbN HEB mixer in a 2.5 THz heterodyne receiver and investigated its performance. This yields important information for future development of heterodyne receivers such as GREAT (German receiver for astronomy at THz frequencies aboard SOFIA) [1] and TELIS (Terahertz limb sounder), a balloon borne heterodyne receiver for atmospheric research [2]. Both are currently under development at DLR.
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Semenov, A., Hübers, H. - W., Engel, A., & Gol'tsman, G. N. (2002). Background limited superconducting quantum detector for astronomy. In NASA/ADS.
Abstract: We present the concept of the superconducting quantum detector for astronomy. Response to a single absorbed photon appears due to successive formation of a normal spot and phase-slip-centers in a narrow strip carrying sub-critical supercurrent. The detector simultaneously has a moderate energy resolution and a variable cut-off wavelength depending on both the material used and operation conditions. We simulated performance of the background-limited direct detector having the 100- micrometer cut-off wavelength. Low dark count rate will allow to realize 10-21 W Hz-1/2 noise equivalent power at 4 K background radiation. The intrinsic recovery time of the counter is rather determined by diffusion of nonequilibrium electrons, thus, thermal fluctuations do not hamper energy resolution of the detector. Provided an appropriate readout technique, the resolution should be better than 1/20 at 50- micrometer wavelength. Planar layout and relatively simple technology favor integration of the detector into an array.
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