Il'in KS, Gol'tsman GN, Voronov BM, Sobolewski R. Characterization of the electron energy relaxation process in NbN hot-electron devices. In: Proc. 10th Int. Symp. Space Terahertz Technol.; 1999. p. 390–7.
Abstract: We report on transient measurements of electron energy relaxation in NbN films with 300-fs time resolution. Using an electro-optic sampling technique, we have studied the photoresponse of 3.5-nm-thick NbN films deposited on sapphire substrates and exposed to 100-fs-wide optical pulses. Our experimental data analysis was based on the two-temperature model and has shown that in our films at the superconducting transition 10.5 K the inelastic electron-phonon scattering time was about (111}+-__.2) ps. This response time indicated that the maximum intermediate-frequency band of a NbN hot-electron phonon-cooled mixer should reach (16+41-3) GHz if one eliminates the bolometric phonon-heating effect. We have suggested several ways to increase the effectiveness of phonon cooling to achieve the above intrinsic value of the NbN mixer bandwidth.
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Blundell R, Kawamura JH, Tong CE, Papa DC, Hunter TR, Gol’tsman GN, et al. A hot-electron bolometer mixer receiver for the 680-830 GHz frequency range. In: Proc. 6-th Int. Conf. Terahertz Electron. IEEE; 1998. p. 18–20.
Abstract: We describe a heterodyne receiver designed to operate in the partially transparent atmospheric windows centered on 680 and 830 GHz. The receiver incorporates a niobium nitride thin film, cooled to 4.2 K, as the phonon-cooled hot-electron mixer element. The double sideband receiver noise, measured over the frequency range 680-830 GHz, is typically 700-1300 K. The instantaneous output bandwidth of the receiver is 600 MHz. This receiver has recently been used at the SubMillimeter Telescope, jointly operated by the Steward Observatory and the Max Planck Institute for Radioastronomy, for observations of the neutral carbon and CO spectral lines at 810 GHz and at 806 and 691 GHz respectively. Laboratory measurements on a second mixer in the same test receiver have yielded extended high frequency performance to 1 THz.
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Svechnikov S, Verevkin A, Voronov B, Menschikov E, Gershenzon E, Gol'tsman G. Quasioptical phonon-cooled NbN hot electron bolometer mixers at 0.5-1.1 THz. In: Proc. 9th Int. Symp. Space Terahertz Technol.; 1998. p. 45–51.
Abstract: The noise performance of a receiver incorporating spiral antenna coupled NbN phonon-cooled superconducting hot electron bolometric mixer is measured from 450 GHz to 1200 GHz. The mixer element is thin (thickness nm) NbN 1.5 pm wide and 0.2 i.um long film fabricated by lift-off e-beam lithography on high-resistive silicon substrate. The noise of the receiver temperature is 1000 K at 800-900 GHz, 1200 K at 950 GHz, and 1600 K at 1.08 THz. The required (absorbed) local-oscillator power is —20 nW.
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Gousev YP, Olsson HK, Gol'tsman GN, Voronov BM, Gershenzon EM. NbN hot-electron mixer at radiation frequencies between 0.9 THz and 1.2 THz. In: Proc. 9th Int. Symp. Space Terahertz Technol.; 1998. p. 121–9.
Abstract: We report on noise temperature measurements for a NbN phonon-cooled hot-electron mixer at radiation frequencies between 0.9 THz and 1.2 THz. Radiation was coupled to the mixer, placed in a vacuum chamber of He cryostat, by means of a planar spiral antenna and a Si immersion lens. A backward-wave oscillator, tunable throughout the spectral range, delivered an output power of few 1.1W that was enough for optimum operation of the mixer. At 4.2 K ambient temperature and 1.025 THz radiation frequency, we obtained a receiver noise temperature of 1550 K despite of using a relatively noisy room-temperature amplifier at the intermediate frequency port. The noise temperature was fairly constant throughout the entire operation range and for intermediate frequencies from 1 GHz to 2 GHz.
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Gerecht E, Musante CF, Yngvesson KS, Waldman J, Gol'tsman GN, Yagoubov PA, et al. Optical coupling and conversion gain for NbN HEB mixer at THz frequencies. In: Proc. 4-th Int. Semicond. Device Research Symp.; 1997. p. 47–50.
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