Shytov, A. V., Levitov, L. S., & Beenakker, C. W. J. (2002). Electromechanical noise in a diffusive conductor. Phys. Rev. Lett., 88(22).
Abstract: Electrons moving in a conductor can transfer momentum to the lattice via collisions with impurities and boundaries, giving rise to a fluctuating mechanical stress tensor. The root-mean-squared momentum transfer per scattering event in a disordered metal (of dimension L greater than the mean free path l and screening length xi) is found to be reduced below the Fermi momentum by a factor of order l/L for shear fluctuations and (xi/L)^2 for pressure fluctuations. The excitation of an elastic bending mode by the shear fluctuations is estimated to fall within current experimental sensitivity for a nanomechanical oscillator.
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Hübers, H. - W., Semenov, A., Richter, H., Smirnov, K., Gol'tsman, G., & Voronov, B. (2002). Phonon cooled far-infrared hot electron bolometer mixer. In NASA/ADS.
Abstract: Heterodyne receivers for applications in astronomy need quantum-limited sensitivity. At frequencies above 1.4 THz superconducting hot electron bolometers (HEB) can be used to achieve this goal. We present results of the development of a quasi-optical phonon-cooled NbN HEB mixer for GREAT, the German heterodyne receiver for SOFIA. Different mixers with logarithmic spiral and double slot feed antennas have been investigated with respect to their noise temperature, conversion loss, linearity and beam pattern at several frequencies between 0.7 THz and 5.2 THz. At 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 16 dB. The response of the mixer was linear up to 400 K load temperature. This performance was verified by measuring an emission line of methanol at 2.5 THz. The results demonstrate that the NbN HEB is very well suited as a mixer for FIR heterodyne receivers.
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Zhou, Y. D., Becker, C. R., Ashokan, R., Selamet, Y., Chang, Y., Boreiko, R. T., et al. (2002). Progress in far-infrared detection technology. In Proc. SPIE (Vol. 4795, pp. 121–128). Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series.
Abstract: II-VI intrinsic very long wavelength infrared (VLWIR, λc~20 to 50 μm) materials, HgCdTe alloys as well as HgCdTe/CdTe superlattices, were grown by molecular beam epitaxy (MBE). The layers were characterized by means of X-ray diffraction, conventional Fourier transform infrared spectroscopy, Hall effect measurements and transmittance electron microscopy (TEM). Photoconductor devices were processed and their spectral response was also measured to demonstrate their applicability in the VLWIR region.
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Deang, J., Du, Q., & Gunzburger, M. D. (2002). Modeling and computation of random thermal fluctuations and material defects in the Ginzburg–Landau model for superconductivity. J. Comp. Phys., 181(1), 45–67.
Abstract: It is well known that thermal fluctuations and material impurities affect the motion of vortices in superconductors. These effects are modeled by variants of a time-dependent Ginzburg-Landau model containing either additive or multiplicative noise. Numerical computations are presented that illustrate the effects that noise has on the dynamics of vortex nucleation and vortex motion. For an additive noise model with relatively low variances, it is found that the vortices form a quasi-steady-state lattice in which the vortex core sizes remain roughly fixed but their positions vibrate. Two multiplicative noise models are considered. For one model having relatively long-range order, the sizes of the vortex cores vary in time and from one vortex to another. Finally, for the additive noise case, we show that as the variance of the noise tends to zero, solutions of the stochastic time-dependent Ginzburg-Landau equations converge to solutions of the corresponding equations with no noise.
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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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Semenov, A. D., Gol'tsman, G. N., & Sobolewski, R. (2002). Hot-electron effect in superconductors and its applications for radiation sensors. Supercond. Sci. Technol., 15(4), R1–R16.
Abstract: The paper reviews the main aspects of nonequilibrium hot-electron phenomena in superconductors and various theoretical models developed to describe the hot-electron effect. We discuss implementation of the hot-electron avalanche mechanism in superconducting radiation sensors and present the most successful practical devices, such as terahertz mixers and direct intensity detectors, for far-infrared radiation. Our presentation also includes the novel approach to hot-electron quantum detection implemented in superconducting x-ray to optical photon counters.
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Ito, H. (2002). High frequency photodiode work in Japan.
Abstract: The recent progress in the device performance of the uni-traveling-carrier photodiode (UTC-PD) is described. The UTC-PD utilizes only electrons as the active carriers, and this unique feature is the key to achieving excellent high-speed and high-output characteristics simultaneously. The achieved performance includes a record 3-dB bandwidth of 310 GHz, high-power photonic millimeter-wave generation with an output power of over +13 dBm at 100 GHz, high-output-voltage photoreceiver operation at bit rates of up to 80 Gbit/s, and demultiplexing operation at 200 Gbit/s using a monolithic PD-EAM optical gate.
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Kawamura, J., Hunter, T. R., Tong, C. Y. E., Blundell, R., Papa, D. C., Patt, F., et al. (2002). Ground-based terahertz CO spectroscopy towards Orion. A&A, 394(1), 271–274.
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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Semenov, A. D., Hübers, H. - W., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2002). 2.5 THz heterodyne receiver with NbN hot-electron-bolometer mixer. Phys. C: Supercond., 372-376, 448–453.
Abstract: We describe a 2.5 THz heterodyne receiver for applications in astronomy and atmospheric research. The receiver employs a superconducting NbN phonon-cooled hot-electron-bolometer mixer and an optically pumped far-infrared gas laser as local oscillator. 2200 K double sideband mixer noise temperature was measured at 2.5 THz across a 1 GHz intermediate frequency bandwidth centred at 1.5 GHz. The total conversion losses were 17 dB. The mixer response was linear at load temperatures smaller than 400 K. The receiver was tested in the laboratory environment by measuring the methanol line in emission. Observed pressure broadening confirms the true heterodyne detection regime of the mixer.
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Meledin, D., Tong, C. Y. - E., Blundell, R., Kaurova, N., Smirnov, K., Voronov, B., et al. (2002). The sensitivity and IF bandwidth of waveguide NbN hot electron bolometer mixers on MgO buffer layers over crystalline quartz. In Harvard university (Ed.), Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 65–72). Cambridge, MA, USA.
Abstract: We have developed and characterized waveguide phonon-cooled NbN Hot Electron Bolometer (FMB) mixers fabricated from a 3-4 nm thick NbN film deposited on a 200nm thick MgO buffer layer over crystalline quartz. Double side band receiver noise temperatures of 900-1050 K at 1.035 THz, and 1300-1400 K at 1.26 THz have been measured at an intermediate frequency of 1.5 GHz. The intermediate frequency bandwidth, measured at 0.8 THz LO frequency, is 3.2 GHz at the optimal bias point for low noise receiver operation.
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