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Nebosis RS, Semenov AD, Gousev YP, Renk KF. Rigorous analysis of a superconducting hot-electron bolometer mixer: theory and comparision with experiment. In: Proc. 7th Int. Symp. Space Terahertz Technol. Charlottesville, Virginia, USA; 1996. p. 601–13.
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Semenov AD, Sergeev AV, Kouminov P, Goghidze IG, Heusinger MA, Nebosis RS, et al. Transparency of YBCO film/substrate interfaces for thermal phonons determined by photoresponse measurements. In: Freyhardt HC, editor. Proc. 1st European Conf. on Appl. Supercond. Vol 2.; 1993. p. 1443–6.
Abstract: Direct measurements of the thermal boundary resistance were performed by means of the stationary method. In this approach the temperature of an electrically heated film is controlled by its dc resistance while an additional film on the same substrate is used as a thermometer monitoring substrate temperature. The temperature field in the substrate is then calculated to deduce the Kapitza temperature step at the interface between the heated strip and the substrate. The main statement of all afore-said papers is that experimental values of the thermal boundary resistance are too large to be explained by the acoustic mismatch model. In this paper we investigate transparency of YBaCuO film/substrate interfaces for thermal phonons by means of photoresponse measurements. We show that our data are in reasonable agreement with the acoustic mismatch theory.
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Gousev YP, Gol'tsman GN, Semenov AD, Gershenzon EM, Nebosis RS, Heusinger MA, et al. Broadband ultrafast superconducting NbN detector for electromagnetic radiation. J Appl Phys. 1994;75(7):3695–7.
Abstract: An ultrafast detector that is sensitive to radiation in a broad spectral range from submillimeter waves to visible light is reported. It consists of a structured NbN thin film cooled to a temperature below Tc (∼11 K). Using 20 ps pulses of a GaAs laser, we observed signal pulses with both rise and decay time of about 50 ps. From the analysis of a mixing experiment with submillimeter radiation we estimate an intrinsic response time of the detector of ∼12 ps. The sensitivity was found to be similar for the near‐infrared and submillimeter radiation. Broadband sensitivity and short response time are attributed to a quasiparticle heating effect.
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Semenov AD, Nebosis RS, Gousev YP, Heusinger MA, Renk KF. Analysis of the nonequilibrium photoresponse of superconducting films to pulsed radiation by use of a two-temperature model. Phys Rev B. 1995;52(1):581–90.
Abstract: Photoresponse of a superconducting film in the resistive state to pulsed radiation has been studied in the framework of a model assuming that two different effective temperatures can be assigned to the quasiparticle and phonon nonequilibrium distributions. The coupled electron-phonon-substrate system is described by a system of time-dependent energy-balance differential equations for effective temperatures. An analytical solution of the system is given and calculated voltage transients are compared with experimental photoresponse signals taking into account the radiation pulse shape and the time resolution of the readout electronics. It is supposed that a resistive state (vortices, fluxons, network of intergrain junctions, hot spots, phase slip centers) provides an ultrafast connection between electron temperature changes and changes of the film resistance and thus plays a minor role in the temporal evolution of the response. In accordance with experimental observations a two-component response was revealed from simulations. The slower component corresponds to a bolometric mechanism while the fast component is connected with the relaxation of the electron temperature. Calculated photoresponse transients are presented for different ratios of the electron and phonon specific heat, radiation pulse durations and fluences, and frequency band passes of registration electronics. From the amplitude of the bolometric component we determine the radiation energy absorbed in a film. This enables us to reveal an intrinsic electron-phonon scattering time even if it is much shorter than the time resolution of readout electronics. We analyze experimental voltage transients for NbN, YBa2Cu3O7, and TlBa2Ca2Cu3O9 superconducting films and find the electron-phonon interaction times at the transition temperatures of 17, 2.5, and 1.8 ps, respectively. The values are in reasonable agreement with data of other experiments.
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Gousev YP, Semenov AD, Pechen EV, Varlashkin AV, Nebosis RS, Renk K. F. Coupling of terahertz radiation to a high-Т(с) superconducting hot electron bolometer mixer. Appl Phys Lett,. 1996;69:691–3.
Abstract: We report on efficient coupling of THz radiation to a high-T(c) superconducting hot electron bolometer that is suitable for heterodyne detection. Our quasioptical system consisted of a planar self-complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co-planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of 0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of'160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of 30 000 K. We also discuss possibilities of significant improvement of the sensitivity.
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