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Author Cherednichenko, S.; Drakinskiy, V.; Baubert, J.; Lecomte, B.; Dauplay, F.; Krieg, J.-M.; Delorme, Y.; Feret, A.; Hübers, H.-W.; Semenov, A. D.; Gol’tsman, G. N. url  openurl
  Title 2.5 THz multipixel heterodyne receiver based on NbN HEB mixers Type Abstract
  Year 2007 Publication Proc. 18th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 18th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 112  
  Keywords NbN HEB mixers  
  Abstract A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4 / SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. Measurements of the mixers sensitivity and the input RF band are presented, and compared against calculations.  
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  Notes Approved no  
  Call Number Serial 1419  
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Author Semenov, A.; Richter, H.; Smirnov, A.; Günther, B.; Hübers, H.-W.; Il’in, K.; Siegel, M.; Gol’tsman, G.; Drakinskiy, V.; Merkel, H.; Karamarkovic, J. url  openurl
  Title Development of HEB mixers for GREAT and for security screening Type Abstract
  Year 2007 Publication Proc. 18th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 18th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 184  
  Keywords NbN HEB mixers, GREAT  
  Abstract We report the study on the quasioptical coupling efficiency and the gain bandwidth of NbN hot-electron bolometer mixers developed for the 4.7 THz channel of the German receiver for Astronomy at THz-frequencies (GREAT) and for security screening at subterahertz frequencies. Radiation coupling efficiency and directive properties of integrated lens antennas with log-spiral, log-periodic and double-slot planar feeds coupled to a hot-electron bolometer were experimentally studied at frequencies from 1 THz to 6 THz and compared with simulations based on the method of moments and the physical-optics ray tracing. For all studied antennas the modeled spectral dependence of the coupling efficiency fits to the experimental data obtained with both Fourier transform spectroscopy and noise temperature measurements only if the complex impedance of the bolometer is explicitly taken into account. Our experimental data did not indicate any noticeable contribution of the quantum noise to the system noise temperature. The experimentally observed deviation of the beam pattern from the model prediction increases with frequency and is most likely due to a non- ideality of the presently used lenses. Study of the intermediate frequency mixer gain at local oscillator (LO) frequencies between 2.5 THz and 0.3 THz showed an increase of the gain bandwidth at low LO frequencies that was understood as the contribution of the direct interaction of magnetic vortices with the radiation field. We have found that the non- homogeneous hot-spot model more adequately describes variation of the intermediate frequency bandwidth with the applied local oscillator power than any of uniform mixer models. The state-of-the-day performance of the GREAT 4.7-THz channel and the 0.8-THz security scanner will be presented.  
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  Notes Approved no  
  Call Number Serial 1420  
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Author Ryabchun, Sergey; Tong, Cheuk-yu Edward; Blundell, Raymond; Kimberk, Robert; Gol’tsman, Gregory url  openurl
  Title Stabilisation of a terahertz hot-electron bolometer mixer with microwave feedback control Type Conference Article
  Year 2007 Publication Proc. 18th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 18th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 193-198  
  Keywords waveguide NbN HEB mixers, Allan variance, stability  
  Abstract We report on implementation of microwave feedback control loop to stabilise the performance of an HEB mixer receiver. It is shown that the receiver sensitivity increases by a factor of 4 over a 16-minute scan, and the corresponding Allan time increases up to 10 seconds, as opposed to an open loop value of 1 second. Our experiments also demonstrate that the receiver sensitivity is limited by the intermediate frequency chain.  
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  Notes Approved no  
  Call Number Serial 1421  
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Author Gol’tsman, G. N. url  openurl
  Title The “Millimetron” project, a future space telescope mission Type Abstract
  Year 2007 Publication Proc. 18th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 18th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 255  
  Keywords Millimetron space observatory, VLBI  
  Abstract The goal of the Millimetron project is to develop a space observatory operating in the millimeter, sub-millimeter and infrared wavelength ranges using a 12-m actively cooled telescope in a single-dish mode and as an interferometer with the space-ground and space-space baselines (the later after the launch of the second identical space telescope). The Millimetron’s main reflector and other optics will be cooled down to 4K thus enabling astronomical observations with super high sensitivity in MM and subMM (down to nanoJansky level). Heterodyne observations in an interferometer mode at frequencies 0.1-1 THz will provide super high angular resolution. The main instruments, planned to be installed are wide-range imaging arrays, radiometers with spectrometers and polarimeters, VLBI heterodyne receivers, and Mikelson type interferometer devices. Wide-range MM and subMM imaging arrays and spectrometers will be based on a superconducting hot electron direct detectors with Andreev mirrors operating at 0.1 K. Such detectors are the best candidates to reach the noise equivalent power level of 10 -19 -10 -20 W/√Hz. Heterodyne receivers will be both SIS based superconducting integrated receiver with flux-flow oscillator as LO (0.1-0.9 THz range) and HEB based receivers using multiplied Gunn oscillator as LO for 1-2 THz range and quantum cascade lasers as LO for 2-5 THz range. For observations in middle IR region there will be installed large arrays of superconducting single photon detectors, providing imaging with very high dynamic range and ultimate sensitivity.  
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  Call Number Serial 1422  
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Author Kitaygorsky, Jennifer; Komissarov, I.; Jukna, A.; Minaeva, O.; Kaurova, N.; Divochiy, A.; Korneev, A.; Tarkhov, M.; Voronov, B.; Milostnaya, I.; Gol'tsman, G.; Sobolewski, R. url  openurl
  Title Fluctuations in two-dimensional superconducting NbN nanobridges and nanostructures meanders Type Abstract
  Year 2007 Publication Proc. APS March Meeting Abbreviated Journal Proc. APS March Meeting  
  Volume 52 Issue 1 Pages L9.00013  
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  Abstract We have observed fluctuations, manifested as sub-nanosecond to nanosecond transient, millivolt-amplitude voltage pulses, generated in two-dimensional NbN nanobridges, as well as in extended superconducting meander nanostructures, designed for single photon counting. Both nanobridges and nano-stripe meanders were biased at currents close to the critical current and measured in a range of temperatures from 1.5 to 8 K. During the tests, the devices were blocked from all incoming radiation by a metallic enclosure and shielded from any external magnetic fields. We attribute the observed spontaneous voltage pulses to the Kosterlitz-Thouless-type fluctuations, where the high enough applied bias current reduces the binding energy of vortex-antivortex pairs and, subsequently, thermal fluctuations break them apart causing the order parameter to momentarily reduce to zero, which in turn causes a transient voltage pulse. The duration of the voltage pulses depended on the device geometry (with the high-kinetic inductance meander structures having longer, nanosecond, pulses) while their rate was directly related to the biasing current as well as temperature.  
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  Notes Approved no  
  Call Number Serial 1027  
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