307 research outputs found
Observing binary inspiral in gravitational radiation: One interferometer
We investigate the sensitivity of individual LIGO/VIRGO-like interferometers
and the precision with which they can determine the characteristics of an
inspiralling binary system. Since the two interferometers of the LIGO detector
share nearly the same orientation, their joint sensitivity is similar to that
of a single, more sensitive interferometer. We express our results for a single
interferometer of both initial and advanced LIGO design, and also for the LIGO
detector in the limit that its two interferometers share exactly the same
orientation. We approximate the evolution of a binary system as driven
exclusively by leading order quadrupole gravitational radiation. To assess the
sensitivity, we calculate the rate at which sources are expected to be
observed, the range to which they are observable, and the precision with which
characteristic quantities describing the observed binary system can be
determined. Assuming a conservative rate density for coalescing neutron star
binary systems we expect that the advanced LIGO detector will observe
approximately 69~yr with an amplitude SNR greater than 8. Of these,
approximately 7~yr will be from binaries at distances greater than
950~Mpc. We explore the sensitivity of these results to a tunable parameter in
the interferometer design (the recycling frequency). The optimum choice of the
parameter is dependent on the goal of the observations, e.g., maximizing the
rate of detections or maximizing the precision of measurement. We determine the
optimum parameter values for these two cases.Comment: 40 pages (plus 7 figures), LaTeX/REVTEX3.0, NU-GR-
Squeezed Light for the Interferometric Detection of High Frequency Gravitational Waves
The quantum noise of the light field is a fundamental noise source in
interferometric gravitational wave detectors. Injected squeezed light is
capable of reducing the quantum noise contribution to the detector noise floor
to values that surpass the so-called Standard-Quantum-Limit (SQL). In
particular, squeezed light is useful for the detection of gravitational waves
at high frequencies where interferometers are typically shot-noise limited,
although the SQL might not be beaten in this case. We theoretically analyze the
quantum noise of the signal-recycled laser interferometric gravitational-wave
detector GEO600 with additional input and output optics, namely
frequency-dependent squeezing of the vacuum state of light entering the dark
port and frequency-dependent homodyne detection. We focus on the frequency
range between 1 kHz and 10 kHz, where, although signal recycled, the detector
is still shot-noise limited. It is found that the GEO600 detector with present
design parameters will benefit from frequency dependent squeezed light.
Assuming a squeezing strength of -6 dB in quantum noise variance, the
interferometer will become thermal noise limited up to 4 kHz without further
reduction of bandwidth. At higher frequencies the linear noise spectral density
of GEO600 will still be dominated by shot-noise and improved by a factor of
10^{6dB/20dB}~2 according to the squeezing strength assumed. The interferometer
might reach a strain sensitivity of 6x10^{-23} above 1 kHz (tunable) with a
bandwidth of around 350 Hz. We propose a scheme to implement the desired
frequency dependent squeezing by introducing an additional optical component to
GEO600s signal-recycling cavity.Comment: Presentation at AMALDI Conference 2003 in Pis
Sagnac Interferometer as a Speed-Meter-Type, Quantum-Nondemolition Gravitational-Wave Detector
According to quantum measurement theory, "speed meters" -- devices that
measure the momentum, or speed, of free test masses -- are immune to the
standard quantum limit (SQL). It is shown that a Sagnac-interferometer
gravitational-wave detector is a speed meter and therefore in principle it can
beat the SQL by large amounts over a wide band of frequencies. It is shown,
further, that, when one ignores optical losses, a signal-recycled Sagnac
interferometer with Fabry-Perot arm cavities has precisely the same
performance, for the same circulating light power, as the Michelson speed-meter
interferometer recently invented and studied by P. Purdue and the author. The
influence of optical losses is not studied, but it is plausible that they be
fairly unimportant for the Sagnac, as for other speed meters. With squeezed
vacuum (squeeze factor ) injected into its dark port, the
recycled Sagnac can beat the SQL by a factor over the
frequency band 10 {\rm Hz} \alt f \alt 150 {\rm Hz} using the same
circulating power kW as is used by the (quantum limited)
second-generation Advanced LIGO interferometers -- if other noise sources are
made sufficiently small. It is concluded that the Sagnac optical configuration,
with signal recycling and squeezed-vacuum injection, is an attractive candidate
for third-generation interferometric gravitational-wave detectors (LIGO-III and
EURO).Comment: 12 pages, 6 figure
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
Experimental demonstration of a squeezing enhanced power recycled Michelson interferometer for gravitational wave detection
Interferometric gravitational wave detectors are expected to be limited by
shot noise at some frequencies. We experimentally demonstrate that a power
recycled Michelson with squeezed light injected into the dark port can overcome
this limit. An improvement in the signal-to-noise ratio of 2.3dB is measured
and locked stably for long periods of time. The configuration, control and
signal readout of our experiment are compatible with current gravitational wave
detector designs. We consider the application of our system to long baseline
interferometer designs such as LIGO.Comment: 4 pages 4 figure
Simulating a dual-recycled gravitational wave interferometer with realistically imperfect optics
We simulate the performance of a gravitational wave interferometer in the
Dual Recycling (DR) configuration, as will be used for systems like
Advanced-LIGO. Our grid-based simulation program models complex interferometric
detectors with realistic optical deformations (e.g., fine-scale mirror surface
roughness). Broadband and Tuned DR are modeled here; the results are also
applied qualitatively to Resonant Sideband Extraction (RSE). Several beneficial
properties anticipated for DR detectors are investigated: signal response
tuning and narrowbanding, power loss reduction, and the reclamation of lost
power as useful light for signal detection. It is shown that these benefits
would be limited by large scattering losses in large (multi-kilometer) systems.
Furthermore, losses may be resonantly enhanced (particularly for RSE), if the
interferometer's modal resonance conditions are not well chosen. We therefore
make two principal recommendations for DR/RSE interferometers: the DR/RSE
cavity must be modally nondegenerate; and fabricated mirror surfaces and
coatings must be as smooth as is practically feasible.Comment: 50 pages, 11 figure
Quantum noise in second generation, signal-recycled laser interferometric gravitational-wave detectors
It has long been thought that the sensitivity of laser interferometric
gravitational-wave detectors is limited by the free-mass standard quantum
limit, unless radical redesigns of the interferometers or modifications of
their input/output optics are introduced. Within a fully quantum-mechanical
approach we show that in a second-generation interferometer composed of arm
cavities and a signal recycling cavity, e.g., the LIGO-II configuration, (i)
quantum shot noise and quantum radiation-pressure-fluctuation noise are
dynamically correlated, (ii) the noise curve exhibits two resonant dips, (iii)
the Standard Quantum Limit can be beaten by a factor of 2, over a frequency
range \Delta f/f \sim 1, but at the price of increasing noise at lower
frequencies.Comment: 35 pages, 9 figures; few misprints corrected and some references
adde
Gravitational Radiation from Rotational Instabilities in Compact Stellar Cores with Stiff Equations of State
We carry out 3-D numerical simulations of the dynamical instability in
rapidly rotating stars initially modeled as polytropes with n = 1.5, 1.0, and
0.5. The calculations are done with a SPH code using Newtonian gravity, and the
gravitational radiation is calculated in the quadrupole limit. All models
develop the global m=2 bar mode, with mass and angular momentum being shed from
the ends of the bar in two trailing spiral arms. The models then undergo
successive episodes of core recontraction and spiral arm ejection, with the
number of these episodes increasing as n decreases: this results in
longer-lived gravitational wave signals for stiffer models. This instability
may operate in a stellar core that has expended its nuclear fuel and is
prevented from further collapse due to centrifugal forces. The actual values of
the gravitational radiation amplitudes and frequencies depend sensitively on
the radius of the star R_{eq} at which the instability develops.Comment: 39 pages, uses Latex 2.09. To be published in the Dec. 15, 1996 issue
of Physical Review D. 21 figures (bitmapped). Originals available in
compressed Postscript format at ftp://zonker.drexel.edu/papers/bars
Squeezed light in a frontal-phase-modulated signal-recycled interferometer
The application of squeezed Light to a frontal-phase-modulated signal-recycled interferometer is considered. We present a simple model to understand the required spectrum of squeezing so as to make the interferometer more sensitive. In particular we analyze the broad-and narrow-band cases for signal recycling and fmd that the sensitivity of the detector can be enhanced provided an appropriate input squeezed spectrum is used. We also discuss the effect of using squeezed light on the bandwidth of the detector
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