1,224 research outputs found
Radiation Pressure Induced Instabilities in Laser Interferometric Detectors of Gravitational Waves
The large scale interferometric gravitational wave detectors consist of
Fabry-Perot cavities operating at very high powers ranging from tens of kW to
MW for next generations. The high powers may result in several nonlinear
effects which would affect the performance of the detector. In this paper, we
investigate the effects of radiation pressure, which tend to displace the
mirrors from their resonant position resulting in the detuning of the cavity.
We observe a remarkable effect, namely, that the freely hanging mirrors gain
energy continuously and swing with increasing amplitude. It is found that the
`time delay', that is, the time taken for the field to adjust to its
instantaneous equilibrium value, when the mirrors are in motion, is responsible
for this effect. This effect is likely to be important in the optimal operation
of the full-scale interferometers such as VIRGO and LIGO.Comment: 27 pages, 11 figures, RevTex styl
Optimising the directional sensitivity of LISA
It was shown in a previous work that the data combinations canceling laser
frequency noise constitute a module - the module of syzygies. The cancellation
of laser frequency noise is crucial for obtaining the requisite sensitivity for
LISA. In this work we show how the sensitivity of LISA can be optimised for a
monochromatic source - a compact binary - whose direction is known, by using
appropriate data combinations in the module. A stationary source in the
barycentric frame appears to move in the LISA frame and our strategy consists
of "coherently tracking" the source by appropriately "switching" the data
combinations so that they remain optimal at all times. Assuming that the
polarisation of the source is not known, we average the signal over the
polarisations. We find that the best statistic is the `network' statistic, in
which case LISA can be construed of as two independent detectors. We compare
our results with the Michelson combination, which has been used for obtaining
the standard sensitivity curve for LISA, and with the observable obtained by
optimally switching the three Michelson combinations. We find that for sources
lying in the ecliptic plane the improvement in SNR increases from 34% at low
frequencies to nearly 90% at around 20 mHz. Finally we present the
signal-to-noise ratios for some known binaries in our galaxy. We also show
that, if at low frequencies SNRs of both polarisations can be measured, the
inclination angle of the plane of the orbit of the binary can be estimated.Comment: 16 pages, 8 figures, submitted to Phys Rev
Experimental demonstration of higher-order Laguerre-Gauss mode interferometry
The compatibility of higher-order Laguerre-Gauss (LG) modes with
interferometric technologies commonly used in gravitational wave detectors is
investigated. In this paper we present the first experimental results
concerning the performance of the LG33 mode in optical resonators. We show that
the Pound-Drever-Hall error signal for a LG33 mode in a linear optical
resonator is identical to that of the more commonly used LG00 mode, and
demonstrate the feedback control of the resonator with a LG33 mode. We
succeeded to increase the mode purity of a LG33 mode generated using a
spatial-light modulator from 51% to 99% upon transmission through a linear
optical resonator. We further report the experimental verification that a
triangular optical resonator does not transmit helical LG modes
The Dynamics of Sustained Reentry in a Loop Model with Discrete Gap Junction Resistance
Dynamics of reentry are studied in a one dimensional loop of model cardiac
cells with discrete intercellular gap junction resistance (). Each cell is
represented by a continuous cable with ionic current given by a modified
Beeler-Reuter formulation. For below a limiting value, propagation is found
to change from period-1 to quasi-periodic () at a critical loop length
() that decreases with . Quasi-periodic reentry exists from
to a minimum length () that is also shortening with .
The decrease of is not a simple scaling, but the bifurcation can
still be predicted from the slope of the restitution curve giving the duration
of the action potential as a function of the diastolic interval. However, the
shape of the restitution curve changes with .Comment: 6 pages, 7 figure
Higher order Laguerre-Gauss mode degeneracy in realistic, high finesse cavities
Higher order Laguerre-Gauss (LG) beams have been proposed for use in future
gravitational wave detectors, such as upgrades to the Advanced LIGO detectors
and the Einstein Telescope, for their potential to reduce the effects of the
thermal noise of the test masses. This paper details the theoretical analysis
and simulation work carried out to investigate the behaviour of LG beams in
realistic optical setups, in particular the coupling between different LG modes
in a linear cavity. We present a new analytical approximation to compute the
coupling between modes, using Zernike polynomials to describe mirror surface
distortions. We apply this method in a study of the behaviour of the LG33 mode
within realistic arm cavities, using measured mirror surface maps from the
Advanced LIGO project. We show mode distortions that can be expected to arise
due to the degeneracy of higher order spatial modes within such cavities and
relate this to the theoretical analysis. Finally we identify the mirror
distortions which cause significant coupling from the LG33 mode into other
order 9 modes and derive requirements for the mirror surfaces.Comment: 12 pages Submitted to PRD 19/07/201
A How-To for the Mock LISA Data Challenges
The LISA International Science Team Working Group on Data Analysis
(LIST-WG1B) is sponsoring several rounds of mock data challenges, with the
purpose of fostering development of LISA data-analysis capabilities, and of
demonstrating technical readiness for the maximum science exploitation of the
LISA data. The first round of challenge data sets were released at this
Symposium. We describe the models and conventions (for LISA and for
gravitational-wave sources) used to prepare the data sets, the file format used
to encode them, and the tools and resources available to support challenge
participants.Comment: 10 pages, 1 figure, in Proceedings of the Sixth International LISA
Symposium (AIP, 2006
Improving the Sensitivity of LISA
It has been shown in the past, that the six Doppler data streams obtained
LISA configuration can be combined by appropriately delaying the data streams
for cancelling the laser frequency noise. Raw laser noise is several orders of
magnitude above the other noises and thus it is essential to bring it down to
the level of shot, acceleration noises. A rigorous and systematic formalism
using the techniques of computational commutative algebra was developed which
generates all the data combinations cancelling the laser frequency noise. The
relevant data combinations form a first module of syzygies. In this paper we
use this formalism for optimisation of the LISA sensitivity by analysing the
noise and signal covariance matrices. The signal covariance matrix, averaged
over polarisations and directions, is calculated for binaries whose frequency
changes at most adiabatically. We then present the extremal SNR curves for all
the data combinations in the module. They correspond to the eigenvectors of the
noise and signal covariance matrices. We construct LISA `network' SNR by
combining the outputs of the eigenvectors which improves the LISA sensitivity
substantially. The maximum SNR curve can yield an improvement upto 70 % over
the Michelson, mainly at high frequencies, while the improvement using the
network SNR ranges from 40 % to over 100 %. Finally, we describe a simple toy
model, in which LISA rotates in a plane. In this analysis, we estimate the
improvement in the LISA sensitivity, if one switches from one data combination
to another as it rotates. Here the improvement in sensitivity, if one switches
optimally over three cyclic data combinations of the eigenvector is about 55 %
on an average over the LISA band-width. The corresponding SNR improvement is 60
%, if one maximises over the module.Comment: 16 pages, 10 figures, Submitted to Class. Quant. Gravit
Detection, Measurement and Gravitational Radiation
Here I examine how to determine the sensitivity of the LIGO, VIRGO, and LAGOS
gravitational wave detectors to sources of gravitational radiation by
considering the process by which data are analyzed in a noisy detector. By
constructing the probability that the detector output is consistent with the
presence of a signal, I show how to (1) quantify the uncertainty that the
output contains a signal and is not simply noise, and (2) construct the
probability distribution that the signal parameterization has a certain value.
From the distribution and its mode I determine volumes in parameter
space such that actual signal parameters are in with probability . If
we are {\em designing} a detector, or determining the suitability of an
existing detector for observing a new source, then we don't have detector
output to analyze but are interested in the ``most likely'' response of the
detector to a signal. I exploit the techniques just described to determine the
``most likely'' volumes for detector output corresponding to the source.
Finally, as an example, I apply these techniques to anticipate the sensitivity
of the LIGO and LAGOS detectors to the gravitational radiation from a perturbed
Kerr black hole.Comment: 37 pages (plus 6 figures), LaTeX/REVTE
The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers
In second-generation, ground-based interferometric gravitational-wave
detectors such as Advanced LIGO, the dominant noise at frequencies
Hz to Hz is expected to be due to thermal fluctuations in the
mirrors' substrates and coatings which induce random fluctuations in the shape
of the mirror face. The laser-light beam averages over these fluctuations; the
larger the beam and the flatter its light-power distribution, the better the
averaging and the lower the resulting thermal noise. In semi-infinite mirrors,
scaling laws for the influence of beam shape on the four dominant types of
thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and
substrate thermoelastic) have been suggested by various researchers and derived
with varying degrees of rigour. Because these scaling laws are important tools
for current research on optimizing the beam shape, it is important to firm up
our understanding of them. This paper (1) gives a summary of the prior work and
of gaps in the prior analyses, (2) gives a unified and rigorous derivation of
all four scaling laws, and (3) explores, relying on work by J. Agresti,
deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra
Laser-interferometer gravitational-wave optical-spring detectors
Using a quantum mechanical approach, we show that in a gravitational-wave
interferometer composed of arm cavities and a signal recycling cavity, e.g.,
the LIGO-II configuration, the radiation-pressure force acting on the mirrors
not only disturbs the motion of the free masses randomly due to quantum
fluctuations, but also and more fundamentally, makes them respond to forces as
though they were connected to an (optical) spring with a specific rigidity.
This oscillatory response gives rise to a much richer dynamics than previously
known, which enhances the possibilities for reshaping the LIGO-II's noise
curves. However, the optical-mechanical system is dynamically unstable and an
appropriate control system must be introduced to quench the instability.Comment: 7 pages, 3 figures; to appear in the Proceedings of 4th Edoardo
Amaldi Conference on Gravitational Waves, Perth, Australia, 8-13 July 200
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