22 research outputs found
Ultra-Sensitive Hot-Electron Nanobolometers for Terahertz Astrophysics
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.Comment: 19 pages, 3 color figure
Black Holes in Higher Dimensions
We review black hole solutions of higher-dimensional vacuum gravity, and of
higher-dimensional supergravity theories. The discussion of vacuum gravity is
pedagogical, with detailed reviews of Myers-Perry solutions, black rings, and
solution-generating techniques. We discuss black hole solutions of maximal
supergravity theories, including black holes in anti-de Sitter space. General
results and open problems are discussed throughout.Comment: 76 pages, 14 figures; review article for Living Reviews in
Relativity. v2: some improvements and refs adde
Lawson criterion for ignition exceeded in an inertial fusion experiment
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion
Prospective Performance of Graphene HEB for Ultrasensitive Detection of Sub-mm Radiation
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Thin THz QCL active regions for improved continuous-wave operating temperature
We compare the performance of 10 and 5 μm thick metal-metal waveguide terahertz quantum-cascade laser ridges operating around 2.7 THz and based on a 4-well phonon depopulation active region design. Thanks to reduced heat dissipation and lower thermal resistance, the 5 μm thick material shows an 18 K increase in continuous wave operating temperature compared to the 10 μm material, despite a lower maximum pulsed-mode operating temperature and a larger input power density. A maximum continuous wave operating temperature of 129 K is achieved using the 5 μm thick material and a 15 μm wide ridge waveguide, which lased up to 155 K in the pulsed mode. The use of thin active regions is likely to become increasingly important to address the increasing input power density of emerging 2- and 3-well active region designs that show the highest pulsed operating temperatures