175 research outputs found
Graphene as a Novel Single Photon Counting Optical and IR Photodetector
Bilayer graphene has many unique optoelectronic properties , including a
tuneable band gap, that make it possible to develop new and more efficient
optical and nanoelectronic devices. We have developed a Monte Carlo simulation
for a single photon counting photodetector incorporating bilayer graphene. Our
results show that, conceptually it would be feasible to manufacture a single
photon counting photodetector (with colour sensitivity) from bilayer graphene
for use across both optical and infrared wavelengths. Our concept exploits the
high carrier mobility and tuneable band gap associated with a bilayer graphene
approach. This allows for low noise operation over a range of cryogenic
temperatures, thereby reducing the cost of cryogens with a trade off between
resolution and operating temperature. The results from this theoretical study
now enable us to progress onto the manufacture of prototype photon counters at
optical and IR wavelengths that may have the potential to be groundbreaking in
some scientific research applications.Comment: Conference Proceeding in Graphene-Based Technologies, 201
Einstein Probe - a small mission to monitor and explore the dynamic X-ray Universe
Einstein Probe is a small mission dedicated to time-domain high-energy
astrophysics. Its primary goals are to discover high-energy transients and to
monitor variable objects in the keV X-rays, at higher sensitivity by
one order of magnitude than those of the ones currently in orbit. Its
wide-field imaging capability, featuring a large instantaneous field-of-view
(, sr), is achieved by using established
technology of micro-pore (MPO) lobster-eye optics, thereby offering
unprecedentedly high sensitivity and large Grasp. To complement this powerful
monitoring ability, it also carries a narrow-field, sensitive follow-up X-ray
telescope based on the same MPO technology to perform follow-up observations of
newly-discovered transients. Public transient alerts will be downlinked
rapidly, so as to trigger multi-wavelength follow-up observations from the
world-wide community. Over three of its 97-minute orbits almost the entire
night sky will be sampled, with cadences ranging from 5 to 25 times per day.
The scientific objectives of the mission are: to discover otherwise quiescent
black holes over all astrophysical mass scales by detecting their rare X-ray
transient flares, particularly tidal disruption of stars by massive black holes
at galactic centers; to detect and precisely locate the electromagnetic sources
of gravitational-wave transients; to carry out systematic surveys of X-ray
transients and characterize the variability of X-ray sources. Einstein Probe
has been selected as a candidate mission of priority (no further selection
needed) in the Space Science Programme of the Chinese Academy of Sciences,
aiming for launch around 2020.Comment: accepted to publish in PoS, Proceedings of "Swift: 10 Years of
Discovery" (Proceedings of Science; ed. by P. Caraveo, P. D'Avanzo, N.
Gehrels and G. Tagliaferri). Minor changes in text, references update
The first GCT camera for the Cherenkov Telescope Array
The Gamma Cherenkov Telescope (GCT) is proposed to be part of the Small Size
Telescope (SST) array of the Cherenkov Telescope Array (CTA). The GCT
dual-mirror optical design allows the use of a compact camera of diameter
roughly 0.4 m. The curved focal plane is equipped with 2048 pixels of
~0.2{\deg} angular size, resulting in a field of view of ~9{\deg}. The GCT
camera is designed to record the flashes of Cherenkov light from
electromagnetic cascades, which last only a few tens of nanoseconds. Modules
based on custom ASICs provide the required fast electronics, facilitating
sampling and digitisation as well as first level of triggering. The first GCT
camera prototype is currently being commissioned in the UK. On-telescope tests
are planned later this year. Here we give a detailed description of the camera
prototype and present recent progress with testing and commissioning.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Measurement of the secondary electron emission from CVD diamond films using phosphor screen detectors
Investigation of the secondary emission characteristics of CVD diamond films for electron amplification
a b s t r a c t Chemical vapour deposition (CVD) diamond offers great potential as a low-cost, high-yield, easily manufactured secondary electron emitter for electron multiplication in devices such as photomultiplier tubes. Its potential for high secondary electron yield offers several significant benefits for these devices including higher time resolution, faster signal rise time, reduced pulse height distribution, low noise, and chemical stability. We describe an experiment to characterize the secondary emission yield of CVD diamond manufactured using different processes and process parameters and discuss the degradation of secondary electron yield and experimental difficulties encountered due to unwanted electron beaminduced contamination. We describe techniques utilized to overcome these difficulties, and present measurements of secondary yield from CVD diamond dynodes in reflection mode. We discuss the application of CVD diamond dynode technology, both in reflection and transmission mode, to advanced high-speed imaging and photon-counting detectors and describe future plans in this area
High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet
We report a high-resolution (R=3000-4000) spectroscopic observation of the DA
white dwarf G191-B2B in the extreme ultraviolet band 220-245 A. A low- density
ionised He component is clearly present along the line-of-sight, which if
completely interstellar implies a He ionisation fraction considerably higher
than is typical of the local interstellar medium. However, some of this
material may be associated with circumstellar gas, which has been detected by
analysis of the C IV absorption line doublet in an HST STIS spectrum. A stellar
atmosphere model assuming a uniform element distribution yields a best fit to
the data which includes a significant abundance of photospheric He. The
99-percent confidence contour for the fit parameters excludes solutions in
which photospheric He is absent, but this result needs to be tested using
models allowing abundance gradients.Comment: LATEX format: 10 pages and 3 figures: accepted for publication in the
Astrophysical Journal Letter
The Southern Wide-field Gamma-ray Observatory reach for Primordial Black Hole evaporation
The Southern Wide-field Gamma-ray Observatory (SWGO) is a proposed ground-based gamma-ray detector that will be located in the Southern Hemisphere and is currently in its design phase. In this contribution, we will outline the prospects for Galactic science with this Observatory. Particular focus will be given to the detectability of extended sources, such as gamma-ray halos around pulsars; optimisation of the angular resolution to mitigate source confusion between known TeV sources; and studies of the energy resolution and sensitivity required to study the spectral features of PeVatrons at the highest energies. Such a facility will ideally complement contemporaneous observatories in studies of high energy astrophysical processes in our Galaxy
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