Semenov, A. D., Hübers, H. –W., Schubert, J., Gol'tsman, G. N., Elantiev, A. I., Voronov, B. M., et al. (2000). Frequency dependent noise temperature of the lattice cooled hot-electron terahertz mixer. In Proc. 11th Int. Symp. Space Terahertz Technol. (pp. 39–48).
Abstract: We present the measurements and the theoretical model on the frequency dependent noise temperature of a lattice cooled hot electron bolometer (HEB) mixer in the terahertz frequency range. The experimentally observed increase of the noise temperature with frequency is a cumulative effect of the non-uniform distribution of the high frequency current in the bolometer and the charge imbalance, which occurs near the edges of the normal domain and contacts with normal metal. In addition, we present experimental results which show that the noise temperature of a HEB mixer can be reduced by about 30% due to a Parylene antireflection coating on the Silicon hyperhemispheric lens.
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Hübers, H. - W., Semenov, A. D., Richter, H., Schubert, J., Hadjiloucas, S., Bowen, J. W., et al. (2001). Antenna pattern of the quasi-optical hot-electron bolometric mixer at terahertz frequencies. In Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 286–296). San Diego, CA, USA.
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Huebers, H. - W., Semenov, A., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2003). Superconducting hot electron bolometer as mixer for far-infrared heterodyne receivers. In T. G. Phillips, & J. Zmuidzinas (Eds.), Proc. SPIE (Vol. 4855, pp. 395–401). Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference, 4855. Tucson, USA: SPIE.
Abstract: Heterodyne receivers for applications in astronomy need quantum limited sensitivity. In instruments which are currently under development for SOFIA or Herschel superconducting hot electron bolometers (HEB) will be used to achieve this goal at frequencies above 1.4 THz. We present results of the development of a phonon-cooled NbN HEB mixer for GREAT, the German Receiver for Astronomy at Terahertz Frequencies, which will be flown aboard SOFIA. The mixer is a small superconducting bridge incorporated in a planar feed antenna and a hyperhemispherical lens. 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 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 17 dB. The response of the mixer was linear up to 400 K load temperature. The performance was verified by measuring an emission line of methanol at 2.5 THz. The measured linewidth is in good agreement with the linewidth deduced from pressure broadening measurements at millimeter wavelength. The results demonstrate that the NbN HEB is very well suited as a mixer for far-infrared heterodyne receivers.
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Vachtomin, Y. B., Antipov, S. V., Maslennikov, S. N., Smirnov, K. V., Polyakov, S. L., Kaurova, N. S., et al. (2004). Noise temperature measurements of NbN phonon-cooled hot electron bolometer mixer at 2.5 and 3.8 THz. In Proc. 15th Int. Symp. Space Terahertz Technol. (pp. 236–241). Northampton, Massachusetts, USA.
Abstract: We present the results of noise temperature measurements of NbN phonon-cooled HEB mixers based on a 3.5 nm NbN film deposited on a high-resistivity Si substrate with a 200 nm – thick MgO buffer layer. The mixer element was integrated with a log-periodic spiral antenna. The noise temperature measurements were performed at 2.5 THz and at 3.8 THz local oscillator frequencies for the 3 µm x 0.2 µm active area devices. The best uncorrected receiver noise temperatures found for these frequencies are 1300 K and 3100 K, respectively. A water vapour discharge laser was used as the LO source. We also present the results of direct detection contribution to the measured Y-factor and of a possible error of noise temperature calculation. This error was more than 8% for the mixer with in-plane dimensions of 2.4 x 0.16 µm 2 at the optimal noise temperature point. The use of a mesh filter enabled us to avoid the effect of direct detection and decrease optical losses by 0.5 dB. The paper is concluded by the investigation results of the mixer polarization response. It was shown that the polarization can differ from the circular one at 3.8 THz by more than 2 dB.
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Antipov, S. V., Vachtomin, Y. B., Maslennikov, S. N., Smirnov, K. V., Kaurova, N. S., Grishina, E. V., et al. (2004). Noise performance of quasioptical ultrathin NbN hot electron bolometer mixer at 2.5 and 3.8 THz. In Proc. 5-th MSMW (Vol. 2, pp. 592–594). Kharkov, Ukraine.
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.
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