Klapwijk TM, Semenov AV. Engineering physics of superconducting hot-electron bolometer mixers. IEEE Trans THz Sci Technol. 2017;7(6):627–48.
Abstract: Superconducting hot-electron bolometers are presently the best performing mixing devices for the frequency range beyond 1.2 THz, where good-quality superconductor-insulator-superconductor devices do not exist. Their physical appearance is very simple: an antenna consisting of a normal metal, sometimes a normal-metal-superconductor bilayer, connected to a thin film of a narrow short superconductor with a high resistivity in the normal state. The device is brought into an optimal operating regime by applying a dc current and a certain amount of local-oscillator power. Despite this technological simplicity, its operation has found to be controlled by many different aspects of superconductivity, all occurring simultaneously. A core ingredient is the understanding that there are two sources of resistance in a superconductor: a charge-conversion resistance occurring at a normal-metal-superconductor interface and a resistance due to time-dependent changes of the superconducting phase. The latter is responsible for the actual mixing process in a nonuniform superconducting environment set up by the bias conditions and the geometry. The present understanding indicates that further improvement needs to be found in the use of other materials with a faster energy relaxation rate. Meanwhile, several empirical parameters have become physically meaningful indicators of the devices, which will facilitate the technological developments.
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Semenov AD, Goghidze IG, Gol’tsman GN, Sergeev AV, Gershenzon EM. Evidence for the spectral dependence of nonequilibrium picosecond photoresponse of YBaCuO thin films. Appl Phys Lett. 1993;63(5):681–3.
Abstract: The transient voltage photoresponse of current biased YBaCuO thin films to 20 ps laser pulses of 0.63 and 1.54 μm wavelengths is measured for temperatures around the superconducting transition region. The fast picosecond decay of the response is followed by a slow nanosecond relaxation which is associated with the bolometric effect. The magnitude of the fast component of the response varies in proportion to the square root of wavelength that plausibly reflects multiplication processes of photoexcited electrons via electron–electron scattering and interaction with high energy phonons.
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Semenov AD, Il'in K, Siegel M, Smirnov A, Pavlov S, Richter H, et al. Evidence of non-bolometric mixing in the bandwidth of a hot-electron bolometer. Supercond Sci Technol. 2006;19(10):1051–6.
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Polyakova MI, Florya IN, Semenov AV, Korneev AA, Goltsman GN. Extracting hot-spot correlation length from SNSPD tomography data. In: J. Phys.: Conf. Ser. Vol 1410.; 2019. 012166 (1 to 4).
Abstract: We present data of quantum detector tomography for the samples specifically optimized for this problem. Using this method, we take results of hot-spot correlation length of 17 ± 2 nm.
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Gol’tsman G, Okunev O, Chulkova G, Lipatov A, Dzardanov A, Smirnov K, et al. Fabrication and properties of an ultrafast NbN hot-electron single-photon detector. IEEE Trans Appl Supercond. 2001;11(1):574–7.
Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film’s supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.
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