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Fu K, Zannoni R, Chan C, Adams SH, Nicholson J, Polizzi E, et al. Terahertz detection in single wall carbon nanotubes. Appl Phys Lett. 2008;92(3):033105.
Abstract: It is reported that terahertz radiation from 0.69 to 2.54 THz has been sensitively detected in a device consisting of bundles of carbon nanotubes containing single wall metallic carbon nanotubes, quasioptically coupled through a lithographically fabricated antenna, and a silicon lens. The measured data are consistent with a bolometric detection process in the metallic tubes and the devices show promise for operation well above 4.2 K.
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Siddiqi I, Prober DE. Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection. Appl Phys Lett. 2004;84(8):1404.
Abstract: 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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Kawamura J, Blundell R, Tong C-YE, Papa DC, Hunter TR, Gol'tsman G, et al. First light with an 800 GHz phonon-cooled HEB mixer receiver. In: Proc. 9th Int. Symp. Space Terahertz Technol. Pasadena, California, USA; 1998. p. 35–43.
Abstract: Phonon-cooled superconductive hot-electron bolometric (HEB) mixers are incorporated in a waveguide receiver designed to operate near 800 Gliz. The mixer elements are thin-film nio- bium nitride microbridges with dimensions of 4 nm thickness, 0.2 to 0.3 p.m in length and 2 jun in width. At 780 GHz the best receiver noise temperature is 840 K (DSB). The mixer IF bandwidth is 2.0 GHz, the absorbed LO power is —0.1 1.1W. A fixed-tuned version of the re- ceiver was installed at the Submillimeter Telescope Observatory on Mt. Graham, Arizona, to conduct astronomical observations. These observations represent the first time that a receiver incorporating any superconducting HEB mixer has been used to detect a spectral line of celes- tial origin.
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Wei J, Olaya D, Karasik BS, Pereverzev SV, Sergeev AV, Gershenson ME. Ultrasensitive hot-electron nanobolometers for terahertz astrophysics. Nature Nanotech. 2008;3(8):496–500.
Abstract: The submillimetre or terahertz region of the electromagnetic spectrum contains approximately half of the total luminosity of the Universe and 98% of all the photons emitted since the Big Bang. This radiation is strongly absorbed in the Earth's atmosphere, so space-based terahertz telescopes are crucial for exploring the evolution of the Universe. Thermal emission from the primary mirrors in these telescopes can be reduced below the level of the cosmic background by active cooling, which expands the range of faint objects that can be observed. However, it will also be necessary to develop bolometers – devices for measuring the energy of electromagnetic radiation—with sensitivities that are at least two orders of magnitude better than the present state of the art. To achieve this sensitivity without sacrificing operating speed, two conditions are required. First, the bolometer should be exceptionally well thermally isolated from the environment;
second, its heat capacity should be sufficiently small. Here we demonstrate that these goals can be achieved by building a superconducting hot-electron nanobolometer. Its design eliminates the energy exchange between hot electrons and the leads by blocking electron outdiffusion and photon emission. The thermal conductance between hot electrons and the thermal bath, controlled by electron–phonon interactions, becomes very small at low temperatures (10-16 WK-1 at 40 mK). These devices, with a heat capacity of 10-19 J K-1, are sufficiently sensitive to detect single terahertz photons in submillimetre astronomy and other applications based on quantum calorimetry and photon counting.
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Maezawa H. Application of superconducting hot-electron bolometer mixers for terahertz-band astronomy. IEICE Trans. Electronics. 2015;98(3):196–206.
Abstract: Recently, a next-generation heterodyne mixer detector – a hot electron bolometer (HEB) mixer employing a superconducting microbridge – has gradually opened up terahertz-band astronomy. The surrounding state-of-the-art technologies including fabrication processes, 4 K cryostats, cryogenic low-noise amplifiers, local oscillator sources, micromachining techniques, and spectrometers, as well as the HEB mixers, have played a valuable role in the development of super-low-noise heterodyne spectroscopy systems for the terahertz band. The current developmental status of terahertz-band HEB mixer receivers and their applications for spectroscopy and astronomy with ground-based, airborne, and satellite telescopes are presented.
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