Kopp, V. I., Churikov, V. M., Zhang, G., Singer, J., Draper, C. W., Chao, N., et al. (2007). Chiral fiber gratings: perspectives and challenges for sensing applications. In Proceedings of Third european workshop on optical fibre sensors (Vol. 6619, pp. 66190B–(pp. 1–8)).
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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Korneev, A., Minaeva, O., Divochiy, A., Antipov, A., Kaurova, N., Seleznev, V., et al. (2007). Ultrafast and high quantum efficiency large-area superconducting single-photon detectors. In M. Dusek, M. S. Hillery, W. P. Schleich, I. Prochazka, A. L. Migdall, & A. Pauchard (Eds.), Proc. SPIE (Vol. 6583, 65830I (1 to 9)). Spie.
Abstract: We present our latest generation of superconducting single-photon detectors (SSPDs) patterned from 4-nm-thick NbN films, as meander-shaped 0.5-mm-long and 100-nm-wide stripes. The SSPDs exhibit excellent performance parameters in the visible-to-near-infrared radiation wavelengths: quantum efficiency (QE) of our best devices approaches a saturation level of 30% even at 4.2 K (limited by the NbN film optical absorption) and dark counts as low as 2x10-4 Hz. The presented SSPDs were designed to maintain the QE of large-active-area devices, but, unless our earlier SSPDs, hampered by a significant kinetic inductance and a nanosecond response time, they are characterized by a low inductance and GHz counting rates. We have designed, simulated, and tested the structures consisting of several, connected in parallel, meander sections, each having a resistor connected in series. Such new, multi-element geometry led to a significant decrease of the device kinetic inductance without the decrease of its active area and QE. The presented improvement in the SSPD performance makes our detectors most attractive for high-speed quantum communications and quantum cryptography applications.
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Slysz, W., Wegrzecki, M., Bar, J., Grabiec, P., Gorska, M., Rieger, E., et al. (2007). Fiber-coupled NbN superconducting single-photon detectors for quantum correlation measurements. In M. Dusek, M. S. Hillery, W. P. Schleich, I. Prochazka, A. L. Migdall, & A. Pauchard (Eds.), Proc. SPIE (Vol. 6583, 65830J (1 to 11)). Spie.
Abstract: We have fabricated fiber-coupled superconducting single-photon detectors (SSPDs), designed for quantum-correlationtype experiments. The SSPDs are nanostructured ( 100-nm wide and 4-nm thick) NbN superconducting meandering stripes, operated in the 2 to 4.2 K temperature range, and known for ultrafast and efficient detection of visible to nearinfrared photons with almost negligible dark counts. Our latest devices are pigtailed structures with coupling between the SSPD structure and a single-mode optical fiber achieved using a micromechanical photoresist ring placed directly over the meander. The above arrangement withstands repetitive thermal cycling between liquid helium and room temperature, and we can reach the coupling efficiency of up to 33%. The system quantum efficiency, measured as the ratio of the photons counted by SSPD to the total number of photons coupled into the fiber, in our early devices was found to be around 0.3 % and 1% for 1.55 &mgr;m and 0.9 &mgr;m photon wavelengths, respectively. The photon counting rate exceeded 250 MHz. The receiver with two SSPDs, each individually biased, was placed inside a transport, 60-liter liquid helium Dewar, assuring uninterrupted operation for over 2 months. Since the receiver’s optical and electrical connections are at room temperature, the set-up is suitable for any applications, where single-photon counting capability and fast count rates are desired. In our case, it was implemented for photon correlation experiments. The receiver response time, measured as a second-order photon cross-correlation function, was found to be below 400 ps, with timing jitter of less than 40 ps.
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Koch, M. (2007). Terahertz communications: a 2020 vision. In NATO Security through Science Series (Vol. 2007, pp. 325–338).
Abstract: We discuss basic considerations for potential short-range THz communication systems which may replace or supplement present WLAN systems in 10–15 years from now. On the basis of a few fundamental estimations we show that such a system will need a line-of-sight connection between receiver and emitter. To circumvent the blocking of the direct line-of-sight connection indoor THz communication systems will also have to rely on non-line-of-sight paths which involve reflections off the walls. The reflectivity of the walls can be enhanced by dielectric mirrors. This new scheme makes steerable high-gain antennas a necessity. Hence, a wireless THz communication system can not be a simple extension of the existing technology of today's local area networks. Instead it involves completely new concepts and ideas that have not yet been worked upon.
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Jian Wei, David Olaya, Boris Karasik, Sergey Pereverzev, Andrei Sergeev, & Michael Gershenson. (2007). Ultra-sensitive hot-electron nanobolometers for terahertz astrophysics. ArXiv e-prints, 710.
Abstract: The background-limited spectral imaging of the early Universe requires spaceborne terahertz (THz) detectors with the sensitivity 2-3 orders of magnitude better than that of the state-of-the-art bolometers. To realize this sensitivity without sacrificing operating speed, novel detector designs should combine an ultrasmall heat capacity of a sensor with its unique thermal isolation. Quantum effects in thermal transport at nanoscale put strong limitations on the further improvement of traditional membrane-supported bolometers. Here we demonstrate an innovative approach by developing superconducting hot-electron nanobolometers in which the electrons are cooled only due to a weak electron-phonon interaction. At T<0.1K, the electron-phonon thermal conductance in these nanodevices becomes less than one percent of the quantum of thermal conductance. The hot-electron nanobolometers, sufficiently sensitive for registering single THz photons, are very promising for submillimeter astronomy and other applications based on quantum calorimetry and photon counting.
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Semenov, A., Haas, P., Ilin, K., Hubers, H., Siegel, M., Engel, A., et al. (2007). Energy resolution and sensitivity of a superconducting quantum detector. Phys. C: Supercond., 460-462, 1491–1492.
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Dickert, F. L. (2007). Christoph A. Schalley (Ed.): Analytical methods in supramolecular chemistry. Anal Bioanal Chem, 389(7-8), 2039–2040.
Abstract: This is a review of book.
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Kampfrath, T., Perfetti, L., von Volkmann, K., Aguirre, C. M., Desjardins, P., Martel, R., et al. (2007). Optical response of single-wall carbon nanotube sheets in the far-infrared spectral range from 1 THz to 40 THz. Phys. Stat. Sol. (B), 244(11), 3950–3954.
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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Lieberzeit, P., Afzal, A., Rehman, A., & Dickert, F. (2007). Nanoparticles for detecting pollutants and degradation processes with mass-sensitive sensors. Sensors and Actuators B: Chemical, 127(1), 132–136.
Abstract: Compared with thin films, nanoparticle layers as coatings for QCM offer substantially increased interaction areas and sensitivities with favourable response times. Molybdenum disulphide (MoS2), e.g. has turned out to be a highly suitable material for interacting with thiols. The resulting materials are sufficiently soft according to Pearson to bind sulphur containing compounds reversibly. Depositing MoS2 nanoparticle submonolayers (particle size 200–300 nm) leads to an increase in sensor response by a factor of ten compared to a pure gold layer. Additionally, the nanoparticle layers show fully reversible sensor signals. Particle synthesis can also be combined with the molecular imprinting approach: by a precipitation technique, it is possible to generate molecularly imprinted TiO2 particles for engine oil degradation measurements. Compared with deposited thin layers, particles incorporate oxidised compounds from lubricants by a factor of two better.
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Kooi, J. W., Baselmans, J. J. A., Hajenius, M., Gao, J. R., Klapwijk, T. M., Dieleman, P., et al. (2007). IF impedance and mixer gain of NbN hot electron bolometers. J. Appl. Phys., 101(4), 044511.
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Cherednichenko, S., Drakinskiy, V., Baubert, J., Krieg, J. - M., Voronov, B., Gol'tsman, G., et al. (2007). Gain bandwidth of NbN hot-electron bolometer terahertz mixers on 1.5 μm Si3N4 / SiO2 membranes. J. Appl. Phys., 101(12), 124508 (1 to 6).
Abstract: The gain bandwidth of NbN hot-electron bolometer terahertz mixers on electrically thin Si3N4/SiO2 membranes was experimentally investigated and compared with that of HEB mixers on bulk substrates. A gain bandwidth of 3.5 GHz is achieved on bulk silicon, whereas the gain bandwidth is reduced down to 0.6–0.9 GHz for mixers on 1.5 μm Si3N4/SiO2 membranes. We show that application of a MgO buffer layer on the membrane extends the gain bandwidth to 3 GHz. The experimental data were analyzed using the film-substrate acoustic mismatch approach.
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Novotny, L. (2007). Effective wavelength scaling for optical antennas. Phys. Rev. Lett., 98(26), 266802(1–4).
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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Khosropanah, P., Gao, J. R., Laauwen, W. M., Hajenius, M., & Klapwijk, T. M. (2007). Low noise NbN hot electron bolometer mixer at 4.3 THz. Appl. Phys. Lett., 91, 221111 (1 to 3).
Abstract: We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hnu/2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.
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Zinoni, C., Alloing, B., Li, L. H., Marsili, F., Fiore, A., Lunghi, L., et al. (2007). Single-photon experiments at telecommunication wavelengths using nanowire superconducting detectors. Appl. Phys. Lett., 91(3), 031106 (1 to 3).
Abstract: The authors report fiber-coupled superconducting single-photon detectors with specifications that exceed those of avalanche photodiodes, operating at telecommunication wavelength, in sensitivity, temporal resolution, and repetition frequency. The improved performance is demonstrated by measuring the intensity correlation function g(2)(τ) of single-photon states at 1300nm produced by single semiconductor quantum dots.
This work was supported by Swiss National Foundation through the “Professeur borsier” and NCCR Quantum Photonics program, FP6 STREP “SINPHONIA” (Contract No. NMP4-CT-2005-16433), IP “QAP” (Contract No. 15848), NOE “ePIXnet,” and the Italian MIUR-FIRB program.
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Ejrnaes, M., Cristiano, R., Quaranta, O., Pagano, S., Gaggero, A., Mattioli, F., et al. (2007). A cascade switching superconducting single photon detector. Appl. Phys. Lett., 91(26), 262509 (1 to 3).
Abstract: We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1ns.
This work was performed in the framework of the EU project “SINPHONIA” NMP4-CT-2005-016433.
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