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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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Loudkov, D., Khosropanah, P., Cherednichenko, S., Adam, A., MerkeI, H., Kollberg, E., et al. (2002). Broadband fourier transform spectrometer (FTS) measurements of spiral and double-slot planar antennas at THz frequencies. In Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 373–369).
Abstract: The direct responses of NbN phonon-cooled hot electron bolometer (HEB) mixers, integrated with different planar antennas, are measured, using Fourier Transform Spectrometer (F1S). One spiral antenna and several double slot antennas, designed for 0.6, 1.4, 1.6, 1.8 and 2.5 THz central frequencies, are investigated. The Optimization of the measurement set-up is discussed in terms of the beam splitter and the F11S-to-HEB coupling. The result shows that the spiral antenna is circular polarized and has a bandwidth of about 2 THz. The frequency bands of double slot antennas show some shift from the design values and their relative bandwidth increases by increasing the design frequency. The antenna responses do not depend on the HEB bias point and temperature, as long as the device is in the resistive state.
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Sobolewski, R., Xu, Y., Zheng, X., Williams, C., Zhang, J., Verevkin, A., et al. (2002). Spectral sensitivity of the NbN single-photon superconducting detector. IEICE Trans. Electron., E85-C(3), 797–802.
Abstract: We report our studies on the spectral sensitivity of superconducting NbN thin-film single-photon detectors (SPD's) capable of GHz counting rates of visible and near-infrared photons. In particular, it has been shown that a NbN SPD is sensitive to 1.55-µm wavelength radiation and can be used for quantum communication. Our SPD's exhibit experimentally measured intrinsic quantum efficiencies from 20% at 800 nm up to 1% at 1.55-µm wavelength. The devices demonstrate picosecond response time (<100 ps, limited by our readout system) and negligibly low dark counts. Spectral dependencies of photon counting of continuous-wave, 0.4-µm to 3.5-µm radiation, and 0.63-µm, 1.33-µm, and 1.55-µm laser-pulsed radiations are presented for the single-stripe-type and meander-type devices.
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Okunev, O., Smirnov, K., Chulkova, G., Korneev, A., Lipatov, A., Gol'tsman, G., et al. (2002). Ultrafast NBN hot-electron single-photon detectors for electronic applications. In Abstracts 8-th IUMRS-ICEM.
Abstract: We present a new, simple to manufacture, single-photon detector (SPD), which can work from ultraviolet to near-infrared wavelengths of optical radiation and combines high speed of operation, high quantum efficiency (QE), and very low dark counts. The devices are superconducting and operate at temperature below 5 K. The physics of operation of our SPD is based on formation of a photon-induced resistive hotspot and subsequent appearance of a transient resistive barrier across an ultrathin and submicron-wide superconductor.
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Lipatov, A., Okunev, O., Smirnov, K., Chulkova, G., Korneev, A., Kouminov, P., et al. (2002). An ultrafast NbN hot-electron single-photon detector for electronic applications. Supercond. Sci. Technol., 15(12), 1689–1692.
Abstract: We present the latest generation of our superconducting single-photon detector (SPD), which can work from ultraviolet to mid-infrared optical radiation wavelengths. The detector combines a high speed of operation and low jitter with high quantum efficiency (QE) and very low dark count level. The technology enhancement allows us to produce ultrathin (3.5 nm thick) structures that demonstrate QE hundreds of times better, at 1.55 μm, than previous 10 nm thick SPDs. The best, 10 × 10 μm2, SPDs demonstrate QE up to 5% at 1.55 μm and up to 11% at 0.86 μm. The intrinsic detector QE, normalized to the film absorption coefficient, reaches 100% at bias currents above 0.9 Ic for photons with wavelengths shorter than 1.3 μm.
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