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Siddiqi, I.; Prober, D. E. |
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Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection |
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Journal Article |
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2004 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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84 |
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8 |
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1404 |
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HEB, mixers, dynamic range, saturation, LO power, local oscillator power, Nb |
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The sensitivity of present Nb diffusion-cooled hot-electron bolometer (HEB) mixers is not quantum limited, and can be improved by reducing the superconducting transition temperature TC. Lowering TC reduces thermal fluctuations, resulting in a decrease of the mixer noise temperature TM. However, lower TC mixers have reduced dynamic range and saturate more easily due to background noise. We present 30 GHz microwave measurements on a bilayer HEB system, Nb–Au, in which TC can be tuned with Au layer thickness to obtain the maximum sensitivity for a given noise background. These measurements are intended as a guide for the optimization of THz mixers. Using a Nb–Au mixer with TC = 1.6 K, we obtain TM = 50 K with 2 nW of local oscillator (LO) power. Good mixer performance is observed over a wide range of LO power and bias voltage and such a device should not exhibit saturation in a THz receiver. |
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0003-6951 |
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571 |
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Yu, B; Zeng, F; Yang, Y; Xing, Q; Chechin, A; Xin, X; Zeylikovich, I; Alfano R. R. |
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Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy |
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2004 |
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Biophys. J. |
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86 |
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3 |
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1649-1654 |
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THz applications |
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491 |
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Krasnopolsky, Vladimir A.; Maillard, Jean Pierre; C. Owen, Tobias |
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Detection of methane in the martian atmosphere: evidence for life? |
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Journal Article |
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2004 |
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Icarus |
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Icarus |
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172 |
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2 |
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537-547 |
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FTS, Mars atmosphere, methane absorption lines, IR spectroscopy, infrared spectroscopy, landfill gas |
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Using the Fourier Transform Spectrometer at the Canada–France–Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH4 band at 3.3 μm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH4 mixing ratio is 10±3 ppb. Total photochemical loss of CH4 in the martian atmosphere is equal to View the MathML source, the CH4 lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH4 during its diffusion through the regolith may be significant. There are no processes of CH4 formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of CH4 by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas†on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured CH4 abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases. |
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879 |
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Goltsman, G.; Korneev, A.; Izbenko, V.; Smirnov, K.; Kouminov, P.; Voronov, B.; Kaurova, N.; Verevkin, A.; Zhang, J.; Pearlman, A.; Slysz, W.; Sobolewski, R. |
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Nano-structured superconducting single-photon detectors |
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2004 |
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |
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520 |
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1-3 |
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527-529 |
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NbN SSPD, SNSPD |
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NbN detectors, formed into meander-type, 10×10-μm2 area structures, based on ultrathin (down to 3.5-nm thickness) and nanometer-width (down to below 100 nm) NbN films are capable of efficiently detecting and counting single photons from the ultraviolet to near-infrared optical wavelength range. Our best devices exhibit QE >15% in the visible range and ∼10% in the 1.3–1.5-μm infrared telecommunication window. The noise equivalent power (NEP) ranges from ∼10−17 W/Hz1/2 at 1.5 μm radiation to ∼10−19 W/Hz1/2 at 0.56 μm, and the dark counts are over two orders of magnitude lower than in any semiconducting competitors. The intrinsic response time is estimated to be <30 ps. Such ultrafast detector response enables a very high, GHz-rate real-time counting of single photons. Already established applications of NbN photon counters are non-invasive testing and debugging of VLSI Si CMOS circuits and quantum communications. |
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0168-9002 |
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1495 |
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Author |
Yorke, Harold W.; Paine, Christopher G.; Bradford, Charles M.; Mark Dragovan; Nash, Al E.; Dooley, Jennifer A.; Lawrence, Charles R. |
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Title |
Thermal design trades for SAFIR architecture concepts |
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Conference Article |
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2004 |
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Proc. SPIE |
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5487 |
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1617-1624 |
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RPLAB @ s @ sun_shield_SAFIR_SPIE_2004 |
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340 |
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