536 research outputs found
Resonant speed meter for gravitational wave detection
Gravitational-wave detectors have been well developed and operated with high
sensitivity. However, they still suffer from mirror displacement noise. In this
paper, we propose a resonant speed meter, as a displacement noise-canceled
configuration based on a ring-shaped synchronous recycling interferometer. The
remarkable feature of this interferometer is that, at certain frequencies,
gravitational-wave signals are amplified, while displacement noises are not.Comment: 4 pages, 4 figure
Search templates for stochastic gravitational-wave backgrounds
Several earth-based gravitational-wave (GW) detectors are actively pursuing
the quest for placing observational constraints on models that predict the
behavior of a variety of astrophysical and cosmological sources. These sources
span a wide gamut, ranging from hydrodynamic instabilities in neutron stars
(such as r-modes) to particle production in the early universe. Signals from a
subset of these sources are expected to appear in these detectors as stochastic
GW backgrounds (SGWBs). The detection of these backgrounds will help us in
characterizing their sources. Accounting for such a background will also be
required by some detectors, such as the proposed space-based detector LISA, so
that they can detect other GW signals. Here, we formulate the problem of
constructing a bank of search templates that discretely span the parameter
space of a generic SGWB. We apply it to the specific case of a class of
cosmological SGWBs, known as the broken power-law models. We derive how the
template density varies in their three-dimensional parameter space and show
that for the LIGO 4km detector pair, with LIGO-I sensitivities, about a few
hundred templates will suffice to detect such a background while incurring a
loss in signal-to-noise ratio of no more than 3%.Comment: Revtex, 7 pages, 18 eps figure
Suspensions Thermal Noise in the LIGO Gravitational Wave Detector
We present a calculation of the maximum sensitivity achievable by the LIGO
Gravitational wave detector in construction, due to limiting thermal noise of
its suspensions. We present a method to calculate thermal noise that allows the
prediction of the suspension thermal noise in all its 6 degrees of freedom,
from the energy dissipation due to the elasticity of the suspension wires. We
show how this approach encompasses and explains previous ways to approximate
the thermal noise limit in gravitational waver detectors. We show how this
approach can be extended to more complicated suspensions to be used in future
LIGO detectors.Comment: 28 pages, 13 figure
High-sensitivity tool for studying phonon related mechanical losses in low loss materials
Fundamental mechanical loss mechanisms exist even in very pure materials, for
instance, due to the interactions of excited acoustic waves with thermal
phonons. A reduction of these losses in a certain frequency range is desired in
high precision instruments like gravitational wave detectors. Systematic
analyses of the mechanical losses in those low loss materials are essential for
this aim, performed in a highly sensitive experimental set-up. Our novel method
of mechanical spectroscopy, cryogenic resonant acoustic spectroscopy of bulk
materials (CRA spectroscopy), is well suited to systematically determine losses
at the resonant frequencies of the samples of less than 10^(-9) in the wide
temperature range from 5 to 300 K. A high precision set-up in a specially built
cryostat allows contactless excitation and readout of the oscillations of the
sample. The experimental set-up and measuring procedure are described.
Limitations to our experiment due to external loss mechanisms are analysed. The
influence of the suspension system as well as the sample preparation is
explained.Comment: 4 pages, 3 figures, proceedings of PHONONS07, submitted to Journal of
Physics: Conference Serie
Upper Limit on Gravitational Wave Backgrounds at 0.2 Hz with Torsion-bar Antenna
We present the first upper limit on gravitational wave (GW) backgrounds at an
unexplored frequency of 0.2 Hz using a torsion-bar antenna (TOBA). A TOBA was
proposed to search for low-frequency GWs. We have developed a small-scaled TOBA
and successfully found {\Omega}gw(f) < 4.3 \times 1017 at 0.2 Hz as
demonstration of the TOBA's capabilities, where {\Omega}gw (f) is the GW energy
density per logarithmic frequency interval in units of the closure density. Our
result is the first nonintegrated limit to bridge the gap between the LIGO band
(around 100 Hz) and the Cassini band (10-6 - 10-4 Hz).Comment: 4 pages, 5 figure
Thermal noise of folding mirrors
Current gravitational wave detectors rely on the use of Michelson interferometers. One crucial limitation of their sensitivity is the thermal noise of their optical components. Thus, for example fluctuational deformations of the mirror surface are probed by a laser beam being reflected from the mirrors at normal incidence. Thermal noise models are well evolved for that case but mainly restricted to single reflections. In this work we present the effect of two consecutive reflections under a non-normal incidence onto mirror thermal noise. This situation is inherent to detectors using a geometrical folding scheme such as GEO\,600. We revise in detail the conventional direct noise analysis scheme to the situation of non-normal incidence allowing for a modified weighting funtion of mirror fluctuations. An application of these results to the GEO\,600 folding mirror for Brownian, thermoelastic and thermorefractive noise yields an increase of displacement noise amplitude by 20\% for most noise processes. The amplitude of thermoelastic substrate noise is increased by a factor 4 due to the modified weighting function. Thus the consideration of the correct weighting scheme can drastically alter the noise predictions and demands special care in any thermal noise design process
Internal thermal noise in the LIGO test masses : a direct approach
The internal thermal noise in LIGO's test masses is analyzed by a new
technique, a direct application of the Fluctuation-Dissipation Theorem to
LIGO's readout observable, (longitudinal position of test-mass face,
weighted by laser beam's Gaussian profile). Previous analyses, which relied on
a normal-mode decomposition of the test-mass motion, were valid only if the
dissipation is uniformally distributed over the test-mass interior, and they
converged reliably to a final answer only when the beam size was a
non-negligible fraction of the test-mass cross section. This paper's direct
analysis, by contrast, can handle inhomogeneous dissipation and arbitrary beam
sizes. In the domain of validity of the previous analysis, the two methods give
the same answer for , the spectral density of thermal noise, to within
expected accuracy. The new analysis predicts that thermal noise due to
dissipation concentrated in the test mass's front face (e.g. due to mirror
coating) scales as , by contrast with homogeneous dissipation, which
scales as ( is the beam radius); so surface dissipation could
become significant for small beam sizes.Comment: 6 pages, RevTex, 1 figur
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