36,619 research outputs found
Method and apparatus for background signal reduction in opto-acoustic absorption measurement
The sensitivity of an opto-acoustic absorption detector is increased to make it possible to measure trace amounts of constituent gases. A second beam radiation path is created through the sample cell identical to a first path except as to length, alternating the beam through the two paths and minimizing the detected pressure difference for the two paths while the beam wavelength is tuned away from the absorption lines of the sample. Then with the beam wavelength tuned to the absorption line of any constituent of interest, the pressure difference is a measure of trace amounts of the constituent. The same improved detector may also be used for measuring the absorption coefficient of known concentrations of absorbing gases
The next detectors for gravitational wave astronomy
This paper focuses on the next detectors for gravitational wave astronomy
which will be required after the current ground based detectors have completed
their initial observations, and probably achieved the first direct detection of
gravitational waves. The next detectors will need to have greater sensitivity,
while also enabling the world array of detectors to have improved angular
resolution to allow localisation of signal sources. Sect. 1 of this paper
begins by reviewing proposals for the next ground based detectors, and presents
an analysis of the sensitivity of an 8 km armlength detector, which is proposed
as a safe and cost-effective means to attain a 4-fold improvement in
sensitivity. The scientific benefits of creating a pair of such detectors in
China and Australia is emphasised. Sect. 2 of this paper discusses the high
performance suspension systems for test masses that will be an essential
component for future detectors, while sect. 3 discusses solutions to the
problem of Newtonian noise which arise from fluctuations in gravity gradient
forces acting on test masses. Such gravitational perturbations cannot be
shielded, and set limits to low frequency sensitivity unless measured and
suppressed. Sects. 4 and 5 address critical operational technologies that will
be ongoing issues in future detectors. Sect. 4 addresses the design of thermal
compensation systems needed in all high optical power interferometers operating
at room temperature. Parametric instability control is addressed in sect. 5.
Only recently proven to occur in Advanced LIGO, parametric instability
phenomenon brings both risks and opportunities for future detectors. The path
to future enhancements of detectors will come from quantum measurement
technologies. Sect. 6 focuses on the use of optomechanical devices for
obtaining enhanced sensitivity, while sect. 7 reviews a range of quantum
measurement options
Baseline design of the filters for the LAD detector on board LOFT
The Large Observatory for X-ray Timing (LOFT) was one of the M3 missions
selected for the phase A study in the ESA's Cosmic Vision program. LOFT is
designed to perform high-time-resolution X-ray observations of black holes and
neutron stars. The main instrument on the LOFT payload is the Large Area
Detector (LAD), a collimated experiment with a nominal effective area of ~10 m
2 @ 8 keV, and a spectral resolution of ~240 eV in the energy band 2-30 keV.
These performances are achieved covering a large collecting area with more than
2000 large-area Silicon Drift Detectors (SDDs) each one coupled to a collimator
based on lead-glass micro-channel plates. In order to reduce the thermal load
onto the detectors, which are open to Sky, and to protect them from out of band
radiation, optical-thermal filter will be mounted in front of the SDDs.
Different options have been considered for the LAD filters for best compromise
between high quantum efficiency and high mechanical robustness. We present the
baseline design of the optical-thermal filters, show the nominal performances,
and present preliminary test results performed during the phase A study.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
Nearby stars as gravitational wave detectors
Sun-like stellar oscillations are excited by turbulent convection and have
been discovered in some 500 main sequence and sub-giant stars and in more than
12,000 red giant stars. When such stars are near gravitational wave sources,
low-order quadrupole acoustic modes are also excited above the experimental
threshold of detectability, and they can be observed, in principle, in the
acoustic spectra of these stars. Such stars form a set of natural detectors to
search for gravitational waves over a large spectral frequency range, from
Hz to Hz. In particular, these stars can probe the
Hz -- Hz spectral window which cannot be probed by current
conventional gravitational wave detectors, such as SKA and eLISA. The PLATO
stellar seismic mission will achieve photospheric velocity amplitude accuracy
of . For a gravitational wave search, we will need to achieve
accuracies of the order of , i.e., at least one generation
beyond PLATO. However, we have found that multi-body stellar systems have the
ideal setup for this type of gravitational wave search. This is the case for
triple stellar systems formed by a compact binary and an oscillating star.
Continuous monitoring of the oscillation spectra of these stars to a distance
of up to a kpc could lead to the discovery of gravitational waves originating
in our galaxy or even elsewhere in the universe. Moreover, unlike experimental
detectors, this observational network of stars will allow us to study the
progression of gravitational waves throughout space.Comment: 10 pages, 2 figures and 1 table. Published in The Astrophysical
Journa
Alternative Detection Methods for Highest Energy Neutrinos
Several experimental techniques are currently under development, to measure
the expected tiny fluxes of highest energy neutrinos above 10**18 eV. Projects
in different stages of realisation are discussed here, which are based on
optical and radio as well as acoustic detectors. For the detection of neutrino
events in this energy range a combination of different detector concepts in one
experiment seems to be most promising.Comment: 8 pages, 8 figures, to be published in Nuclear Physics B (Proceedings
Supplement): Proceedings of the XXIst International Conference on Neutrino
Physics and Astrophysics, Paris, June 14-19, 200
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