| Records |
| Author |
Semenov, A.; Haas, P.; Ilin, K.; Hubers, H.; Siegel, M.; Engel, A.; Smirnov, A. |
| Title |
Energy resolution and sensitivity of a superconducting quantum detector |
Type |
Journal Article |
| Year |
2007 |
Publication |
Phys. C: Supercond. |
Abbreviated Journal  |
Phys. C: Supercond. |
| Volume |
460-462 |
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Pages |
1491-1492 |
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| ISSN |
0921-4534 |
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no |
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535 |
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| Author |
Huard, B.; Pothier, H.; Esteve, D.; Nagaev, K. E. |
| Title |
Electron heating in metallic resistors at sub-Kelvin temperature |
Type |
Journal Article |
| Year |
2007 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
76 |
Issue |
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Pages |
165426(1-9) |
| Keywords |
electron heating in resistor, HEB distributed model, HEB model, hot electrons |
| Abstract |
In the presence of Joule heating, the electronic temperature in a metallic resistor placed at sub-Kelvin temperatures can significantly exceed the phonon temperature. Electron cooling proceeds mainly through two processes: electronic diffusion to and from the connecting wires and electron-phonon coupling. The goal of this paper is to present a general solution of the problem in a form that can easily be used in practical situations. As an application, we compute two quantities that depend on the electronic temperature profile: the second and the third cumulant of the current noise at zero frequency, as a function of the voltage across the resistor. We also consider time-dependent heating, an issue relevant for experiments in which current pulses are used, for instance, in time-resolved calorimetry experiments. |
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Recommended by Klapwijk as example for writing the article on the HEB model. |
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936 |
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| Author |
Bell, M.; Sergeev, A.; Mitin, V.; Bird, J.; Verevkin, A.; Gol’tsman, G. |
| Title |
One-dimensional resistive states in quasi-two-dimensional superconductors: Experiment and theory |
Type |
Journal Article |
| Year |
2007 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
76 |
Issue |
9 |
Pages |
094521 (1 to 5) |
| Keywords |
uasi-two-dimensional superconductors, NbN |
| Abstract |
We investigate competition between one- and two-dimensional topological excitations—phase slips and vortices—in the formation of resistive states in quasi-two-dimensional superconductors in a wide temperature range below the mean-field transition temperature TC0. The widths w=100nm of our ultrathin NbN samples are substantially larger than the Ginzburg-Landau coherence length ξ=4nm, and the fluctuation resistivity above TC0 has a two-dimensional character. However, our data show that the resistivity below TC0 is produced by one-dimensional excitations—thermally activated phase slip strips (PSSs) overlapping the sample cross section. We also determine the scaling phase diagram, which shows that even in wider samples the PSS contribution dominates over vortices in a substantial region of current and/or temperature variations. Measuring the resistivity within 7 orders of magnitude, we find that the quantum phase slips can only be essential below this level. |
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1098-0121 |
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no |
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1423 |
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| Author |
Novotny, Lukas |
| Title |
Effective wavelength scaling for optical antennas |
Type |
Journal Article |
| Year |
2007 |
Publication |
Phys. Rev. Lett. |
Abbreviated Journal |
Phys. Rev. Lett. |
| Volume |
98 |
Issue |
26 |
Pages |
266802(1-4) |
| Keywords |
optical antennas |
| Abstract |
In antenna theory, antenna parameters are directly related to the wavelength λ of incident radiation, but this scaling fails at optical frequencies where metals behave as strongly coupled plasmas. In this Letter we show that antenna designs can be transferred to the optical frequency regime by replacing λ by a linearly scaled effective wavelength λeff=n1+n2λ/λp, with λp being the plasma wavelength and n1, n2 being coefficients that depend on geometry and material properties. It is assumed that the antenna is made of linear segments with radii Râ‰<aa>λ. Optical antennas hold great promise for increasing the efficiency of photovoltaics, light-emitting devices, and optical sensors. |
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no |
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RPLAB @ gujma @ |
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749 |
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| Author |
Kampfrath, Tobias; Perfetti, Luca; von Volkmann, Konrad; Aguirre, Carla M.; Desjardins, Patrick; Martel, Richard; Frischkorn, Christian; Wolf, Martin |
| Title |
Optical response of single-wall carbon nanotube sheets in the far-infrared spectral range from 1 THz to 40 THz |
Type |
Journal Article |
| Year |
2007 |
Publication |
Physica Status Solidi (B) |
Abbreviated Journal |
Phys. Stat. Sol. (B) |
| Volume |
244 |
Issue |
11 |
Pages |
3950-3954 |
| Keywords |
single wall, carbon nanotube, SWNT, SWCNT, CNT, detector, sensor, TDS |
| Abstract |
The optical properties of single-wall carbon nanotube sheets in the far-infrared have been investigated with THz time-domain spectroscopy. Over a wide frequency range from 1 THz to 40 THz, the complex dielectric function of the nanotube sample has been derived. Our data can be excellently reproduced by a Drude-Lorentz model function. The extracted fit parameters such as Lorentz resonance frequency and plasma frequency are consistent with values obtained by scanning tunneling techniques. We discuss the origin of both the Lorentz and Drude contribution in terms of direct and indirect optical transitions. |
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0370-1972 |
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no |
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569 |
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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. |
| Title |
2.5 THz multipixel heterodyne receiver based on NbN HEB mixers |
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Abstract |
| Year |
2007 |
Publication |
Proc. 18th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 18th Int. Symp. Space Terahertz Technol. |
| Volume |
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Issue |
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Pages |
112 |
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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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no |
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1419 |
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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. |
| Title |
Development of HEB mixers for GREAT and for security screening |
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Abstract |
| Year |
2007 |
Publication |
Proc. 18th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 18th Int. Symp. Space Terahertz Technol. |
| Volume |
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Pages |
184 |
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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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1420 |
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| Author |
Ryabchun, Sergey; Tong, Cheuk-yu Edward; Blundell, Raymond; Kimberk, Robert; Gol’tsman, Gregory |
| 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 |
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Issue |
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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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1421 |
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Gol’tsman, G. N. |
| Title |
The “Millimetron” project, a future space telescope mission |
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Abstract |
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2007 |
Publication |
Proc. 18th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 18th Int. Symp. Space Terahertz Technol. |
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255 |
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Millimetron space observatory, VLBI |
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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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1422 |
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Kopp, Victor I.; Churikov, Victor M.; Zhang, Guoyin; Singer, Jonathan; Draper, Christopher W.; Chao, Norman; Neugroschl, Daniel; Genack, Azriel Z. |
| Title |
Chiral fiber gratings: perspectives and challenges for sensing applications |
Type |
Conference Article |
| Year |
2007 |
Publication |
Proceedings of Third european workshop on optical fibre sensors |
Abbreviated Journal |
Proc. 3rd European Workshop on Opt. Fibre Sensors |
| Volume |
6619 |
Issue |
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Pages |
66190B-(1-8) |
| Keywords |
optical fiber gratings, chiral fiber gratings applications, chiral gratings applications, from chiralphotonics |
| Abstract |
Chiral fiber gratings are produced in a microforming process in which optical fibers with noncircular or nonconcentric cores are twisted as they pass though a miniature oven. Periodic glass structures as stable as the glass material itself are produced with helical pitch that ranges from under a micron to hundreds of microns. The geometry of the fiber cross section determines the symmetry of the resulting structure which in turn determines its polarization selectivity. Single helix structures are polarization insensitive while double helix gratings interact only with a single optical polarization. Both single and double helix gratings may act as a fiber long period grating, coupling the core and cladding modes. The coupling is manifested in a series of narrow dips in the transmission spectrum. The dip position is sensitive to fiber elongation, twist and temperature, and to the refractive index of the surrounding medium. The suitability of chiral gratings for sensing pressure, temperature and liquid levels is investigated. Polarization insensitive single helix silica glass gratings display excellent stability up to temperatures of 6000C, while a pressure sensor with dynamic range of nearly 40 dB is demonstrated in polarization selective double helix gratings. |
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855 |
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