407 research outputs found
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
QND and higher order effects for a nonlinear meter in an interferometric gravitational wave antenna
A new optical topology and signal readout strategy for a laser interferometer
gravitational wave detector were proposed recently by Braginsky and Khalili .
Their method is based on using a nonlinear medium inside a microwave oscillator
to detect the gravitational-wave-induced spatial shift of the interferometer's
standing optical wave. This paper proposes a quantum nondemolition (QND) scheme
that could be realistically used for such a readout device and discusses a
"fundamental" sensitivity limit imposed by a higher order optical effect.Comment: LaTex, 17 pages, 3 figure
A nonlinear detection algorithm for periodic signals in gravitational wave detectors
We present an algorithm for the detection of periodic sources of
gravitational waves with interferometric detectors that is based on a special
symmetry of the problem: the contributions to the phase modulation of the
signal from the earth rotation are exactly equal and opposite at any two
instants of time separated by half a sidereal day; the corresponding is true
for the contributions from the earth orbital motion for half a sidereal year,
assuming a circular orbit. The addition of phases through multiplications of
the shifted time series gives a demodulated signal; specific attention is given
to the reduction of noise mixing resulting from these multiplications. We
discuss the statistics of this algorithm for all-sky searches (which include a
parameterization of the source spin-down), in particular its optimal
sensitivity as a function of required computational power. Two specific
examples of all-sky searches (broad-band and narrow-band) are explored
numerically, and their performances are compared with the stack-slide technique
(P. R. Brady, T. Creighton, Phys. Rev. D, 61, 082001).Comment: 9 pages, 3 figures, to appear in Phys. Rev.
To the practical design of the optical lever intracavity topology of gravitational-wave detectors
The QND intracavity topologies of gravitational-wave detectors proposed
several years ago allow, in principle, to obtain sensitivity significantly
better than the Standard Quantum Limit using relatively small anount of optical
pumping power. In this article we consider an improved more ``practical''
version of the optical lever intracavity scheme. It differs from the original
version by the symmetry which allows to suppress influence of the input light
amplitude fluctuation. In addition, it provides the means to inject optical
pumping inside the scheme without increase of optical losses.
We consider also sensitivity limitations imposed by the local meter which is
the key element of the intracavity topologies. Two variants of the local meter
are analyzed, which are based on the spectral variation measurement and on the
Discrete Sampling Variation Measurement, correspondingly. The former one, while
can not be considered as a candidate for a practical implementation, allows, in
principle, to obtain the best sensitivity and thus can be considered as an
ideal ``asymptotic case'' for all other schemes. The DSVM-based local meter can
be considered as a realistic scheme but its sensitivity, unfortunately, is by
far not so good just due to a couple of peculiar numeric factors specific for
this scheme.
From our point of view search of new methods of mechanical QND measurements
probably based on improved DSVM scheme or which combine the local meter with
the pondermotive squeezing technique, is necessary.Comment: 27 pages, 6 figure
Past and future gauge in numerical relativity
Numerical relativity describes a discrete initial value problem for general
relativity. A choice of gauge involves slicing space-time into space-like
hypersurfaces. This introduces past and future gauge relative to the
hypersurface of present time. Here, we propose solving the discretized Einstein
equations with a choice of gauge in the future and a dynamical gauge in the
past. The method is illustrated on a polarized Gowdy wave.Comment: To appear in Class Quantum Grav, Let
Adaptive filtering techniques for gravitational wave interferometric data: Removing long-term sinusoidal disturbances and oscillatory transients
It is known by the experience gained from the gravitational wave detector
proto-types that the interferometric output signal will be corrupted by a
significant amount of non-Gaussian noise, large part of it being essentially
composed of long-term sinusoids with slowly varying envelope (such as violin
resonances in the suspensions, or main power harmonics) and short-term ringdown
noise (which may emanate from servo control systems, electronics in a
non-linear state, etc.). Since non-Gaussian noise components make the detection
and estimation of the gravitational wave signature more difficult, a denoising
algorithm based on adaptive filtering techniques (LMS methods) is proposed to
separate and extract them from the stationary and Gaussian background noise.
The strength of the method is that it does not require any precise model on the
observed data: the signals are distinguished on the basis of their
autocorrelation time. We believe that the robustness and simplicity of this
method make it useful for data preparation and for the understanding of the
first interferometric data. We present the detailed structure of the algorithm
and its application to both simulated data and real data from the LIGO 40meter
proto-type.Comment: 16 pages, 9 figures, submitted to Phys. Rev.
Scattering of Woods-Saxon Potential in Schrodinger Equation
The scattering solutions of the one-dimensional Schrodinger equation for the
Woods-Saxon potential are obtained within the position-dependent mass
formalism. The wave functions, transmission and reflection coefficients are
calculated in terms of Heun's function. These results are also studied for the
constant mass case in detail.Comment: 14 page
Speed Meter As a Quantum Nondemolition Measuring Device for Force
Quantum noise is an important issue for advanced LIGO. Although it is in
principle possible to beat the Standard Quantum Limit (SQL), no practical
recipe has been found yet. This paper dicusses quantum noise in the context of
speedmeter-a devise monitoring the speed of the testmass. The scheme proposed
to overcome SQL in this case might be more practical than the methods based on
monitoring position of the testmass.Comment: 7 pages of RevTex, 1 postscript figur
Data analysis of gravitational-wave signals from spinning neutron stars. II. Accuracy of estimation of parameters
We examine the accuracy of estimation of parameters of the gravitational-wave
signals from spinning neutron stars that can be achieved from observations by
Earth-based laser interferometers. We consider a model of the signal consisting
of two narrowband components and including both phase and amplitude modulation.
We calculate approximate values of the rms errors of the parameter estimators
using the Fisher information matrix. We carry out extensive Monte Carlo
simulations and obtain cumulative distribution functions of rms errors of
astrophysically interesting parameters: amplitude of the signal, wobble angle,
position of the source in the sky, frequency, and spindown coefficients. We
consider both all-sky searches and directed searches. We also examine the
possibility of determination of neutron star proper motion. We perform
simulations for all laser-interferometric detectors that are currently under
construction and for several possible lengths of the observation time and sizes
of the parameter space. We find that observations of continuous
gravitational-wave signals from neutron stars by laser-interferometric
detectors will provide a very accurate information about their astrophysical
properties. We derive several simplified models of the signal that can be used
in the theoretical investigations of the data analysis schemes independently of
the physical mechanisms generating the gravitational-wave signal.Comment: LaTeX, 34 pages, 15 figures, submitted to Phys. Rev.
Colliding Black Holes: The Close Limit
The problem of the mutual attraction and joining of two black holes is of
importance as both a source of gravitational waves and as a testbed of
numerical relativity. If the holes start out close enough that they are
initially surrounded by a common horizon, the problem can be viewed as a
perturbation of a single black hole. We take initial data due to Misner for
close black holes, apply perturbation theory and evolve the data with the
Zerilli equation. The computed gravitational radiation agrees with and extends
the results of full numerical computations.Comment: 4 pages, Revtex, 3 postscript figures included, CGPG-94/2-
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