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Yagoubov P, Kroug M, Merkel H, Kollberg E, Schubert J, Hubers HW, et al. Hot electron bolometric mixers based on NbN films deposited on MgO substrates. In: Inst. Phys. Conf. Ser. Vol 167. Barcelona, Spain; 1999. p. 687–90.
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Schubert J, Semenov A, Gol'tsman G, Hübers H-W, Schwaab G, Voronov B, et al. Noise temperature of an NbN hot-electron bolometric mixer at frequencies from 0.7 THz to 5.2 THz. Supercond. Sci. Technol.. 1999;12(11):748–50.
Abstract: We report on noise temperature measurements of an NbN phonon-cooled hot-electron bolometric mixer in the terahertz frequency range. The devices were 3 nm thick films with in-plane dimensions 1.7 × 0.2 µm2 and 0.9 × 0.2 µm2 integrated in a complementary logarithmic-spiral antenna. Measurements were performed at seven frequencies ranging from 0.7 THz to 5.2 THz. The measured DSB noise temperatures are 1500 K (0.7 THz), 2200 K (1.4 THz), 2600 K (1.6 THz), 2900 K (2.5 THz), 4000 K (3.1 THz), 5600 K (4.3 THz) and 8800 K (5.2 THz).
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Tong C-YE, Kawamura J, Todd RH, Papa DC, Blundell R, Smith M, et al. Successful operation of a 1 THz NbN hot-electron bolometer receiver. In: Proc. 11th Int. Symp. Space Terahertz Technol.; 2000. p. 49–59.
Abstract: A phonon-cooled NbN superconductive hot-electron bolometer receiver covering the frequency range 0.8-1.04 THz has successfully been used for astronomical observation at the Sub-Millimeter Telescope Observatory on Mount Graham, Arizona. This waveguide heterodyne receiver is a modified version of our fixed-tuned 800 GHz HEB receiver to allow for operation beyond 1 THz. The measured noise temperature of this receiver is about 1250 K at 0.81 THz, 560 K at 0.84 THz, and 1600 K at 1.035 THz. It has a 1 GHz wide IF bandwidth, centered at 1.8 GHz. This receiver has recently been used to detect the CO (9-8) molecular line emission at 1.037 THz in the Orion nebula. This is the first time a ground-based heterodyne receiver has been used to detect a celestial source above 1 THz.
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Semenov AD, Hübers H–W, Schubert J, Gol'tsman GN, Elantiev AI, Voronov BM, et al. Frequency dependent noise temperature of the lattice cooled hot-electron terahertz mixer. In: Proc. 11th Int. Symp. Space Terahertz Technol.; 2000. p. 39–48.
Abstract: We present the measurements and the theoretical model on the frequency dependent noise temperature of a lattice cooled hot electron bolometer (HEB) mixer in the terahertz frequency range. The experimentally observed increase of the noise temperature with frequency is a cumulative effect of the non-uniform distribution of the high frequency current in the bolometer and the charge imbalance, which occurs near the edges of the normal domain and contacts with normal metal. In addition, we present experimental results which show that the noise temperature of a HEB mixer can be reduced by about 30% due to a Parylene antireflection coating on the Silicon hyperhemispheric lens.
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Semenov AD, Hübers H-W, Schubert J, Gol'tsman GN, Elantiev AI, Voronov BM, et al. Design and performance of the lattice-cooled hot-electron terahertz mixer. J Appl Phys. 2000;88(11):6758–67.
Abstract: We present the measurements and the theoreticalmodel of the frequency-dependent noise temperature of a superconductor lattice-cooled hot-electron bolometer mixer in the terahertz frequency range. The increase of the noise temperature with frequency is a cumulative effect of the nonuniform distribution of the high-frequency current in the bolometer and the charge imbalance, which occurs at the edges of the normal domain and at the contacts with normal metal. We show that under optimal operation the fluctuation sensitivity of the mixer is determined by thermodynamic fluctuations of the noise power, whereas at small biases there appears additional noise, which is probably due to the flux flow. We propose the prescription of how to minimize the influence of the current distribution on the mixer performance.
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Sergeev A, Mitin V. Electron-phonon interaction in disordered conductors: Static and vibrating scattering potentials. Phys Rev B. 2000;61(9):6041–7.
Abstract: Employing the Keldysh diagram technique, we calculate the electron-phonon energy relaxation rate in a conductor with the vibrating and static δ-correlated random electron-scattering potentials. If the scattering potential is completely dragged by phonons, this model yields the Schmid’s result for the inelastic electron-scattering rate τ−1e−ph. At low temperatures the effective interaction decreases due to disorder, and τ−1e−ph∝T4l (l is the electron mean-free path). In the presense of the static potential, quantum interference of numerous scattering processes drastically changes the effective electron-phonon interaction. In particular, at low temperatures the interaction increases, and τ−1e−ph∝T2/l. Along with an enhancement of the interaction, which is observed in disordered metallic films and semiconducting structures at low temperatures, the suggested model allows us to explain the strong sensitivity of the electron relaxation rate to the microscopic quality of a particular film.
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Kroug M, Cherednichenko S, Merkel H, Kollberg E, Voronov B, Gol'tsman G, et al. NbN hot electron bolometric mixers for terahertz receivers. IEEE Trans Appl Supercond. 2001;11(1):962–5.
Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.
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Gershenson ME, Gong D, Sato T, Karasik BS, Sergeev AV. Millisecond electron-phonon relaxation in ultrathin disordered metal films at millikelvin temperatures. Appl. Phys. Lett.. 2001;79:2049–51.
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Kroug M, Cherednichenko S, Choumas M, Merkel H, Kollberg E, Hübers H-W, et al. HEB quasi-optical heterodyne receiver for THz frequencies. In: Proc. 12th Int. Symp. Space Terahertz Technol. San Diego, CA, USA; 2001. p. 244–52.
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Kawamura J, Hunter TR, Tong CYE, Blundell R, Papa DC, Patt F, et al. Ground-based terahertz CO spectroscopy towards Orion. A&A. 2002;394(1):271–4.
Abstract: Using a superconductive hot-electron bolometer heterodyne receiver on the 10-m Heinrich Hertz Telescope on Mount Graham, Arizona, we have obtained velocity-resolved 1.037 THz CO () spectra toward several positions along the Orion Molecular Cloud (OMC-1) ridge. We confirm the general results of prior observations of high-J CO lines that show that the high temperature, , high density molecular gas, , is quite extended, found along a ~ region centered on BN/KL. However, our observations have significantly improved angular resolution, and with a beam size of we are able to spatially and kinematically discriminate the emission originating in the extended quiescent ridge from the very strong and broadened emission originating in the compact molecular outflow. The ridge emission very close to the BN/KL region appears to originate from two distinct clouds along the line of sight with and ≈ . The former component dominates the emission to the south of BN/KL and the latter to the north, with a turnover point coincident with or near BN/KL. Our evidence precludes a simple rotation of the inner ridge and lends support to a model in which there are multiple molecular clouds along the line of sight towards the Orion ridge.
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