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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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Sobolewski, R., Verevkin, A., & Gol’tsman, G. N. (2004). Superconducting optical single-photon detectors. In CLEO/QELS (IThD1). Optical Society of America.
Abstract: We review the development of superconducting single-photon detectors. The devices are characterized by experimental quantum efficiency of ~8% for infrared photons, counting rate ~2 GHz, 18 ps jitter, and <0.01 per second dark counts.
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Slysz, W., Wegrzecki, M., Papis, E., Gol'tsman, G. N., Verevkin, A., & Sobolewski, R. (2004). A method of optimization of the NbN superconducting single-photon detector (Vol. 36).
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Slysz, W., Wegrzecki, M., Bar, J., Grabiec, P., Gol'tsman, G. N., Verevkin, M., et al. (2004). NbN superconducting single-photon detectors coupled with a communication fiber (Vol. 37).
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Siddiqi, I., & Prober, D. E. (2004). Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection. Appl. Phys. Lett., 84(8), 1404.
Abstract: The sensitivity of present Nb diffusion-cooled hot-electron bolometer (HEB) mixers is not quantum limited, and can be improved by reducing the superconducting transition temperature TC. Lowering TC reduces thermal fluctuations, resulting in a decrease of the mixer noise temperature TM. However, lower TC mixers have reduced dynamic range and saturate more easily due to background noise. We present 30 GHz microwave measurements on a bilayer HEB system, Nb–Au, in which TC can be tuned with Au layer thickness to obtain the maximum sensitivity for a given noise background. These measurements are intended as a guide for the optimization of THz mixers. Using a Nb–Au mixer with TC = 1.6 K, we obtain TM = 50 K with 2 nW of local oscillator (LO) power. Good mixer performance is observed over a wide range of LO power and bias voltage and such a device should not exhibit saturation in a THz receiver.
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