8 research outputs found
Angular instability in high optical power suspended cavities
Advanced gravitational wave detectors use suspended test masses to form
optical resonant cavities for enhancing the detector sensitivity. These
cavities store hundreds of kilowatts of coherent light and even higher optical
power for future detectors. With such high optical power, the radiation
pressure effect inside the cavity creates sufficiently strong coupling between
test masses whose dynamics are significantly altered. The dynamics of two
independent nearly free masses become a coupled mechanical resonator system.
The transfer function of the local control system used for controlling the test
masses is modified by the radiation pressure effect. The changes in the
transfer function of the local control systems can result in a new type of
angular instability which occurs at only 1.3 \% of the Sidles-Sigg instability
threshold power. We report experimental results on a 74~m suspended cavity with
a few kilowatts of circulating power, for which the power to mass ratio is
comparable to the current Advanced LIGO. The radiation pressure effect on the
test masses behaves like an additional optical feedback with respect to the
local angular control, potentially making the mirror control system unstable.
When the local angular control system is optimized for maximum stability
margin, the instability threshold power increases from 4~kW to 29~kW. The
system behavior is consistent with our simulation and the power dependent
evolution of both the cavity soft and hard mode is observed. We show that this
phenomenon is likely to significantly affect proposed gravitational wave
detectors that require very high optical power.Comment: 7 pages, 7 figures, accepted for publication in Review of Scientific
Instrument
Characterization of systematic error in Advanced LIGO calibration
The raw outputs of the detectors within the Advanced Laser Interferometer Gravitational-Wave Observatory need to be calibrated in order to produce the estimate of the dimensionless strain used for astrophysical analyses. The two detectors have been upgraded since the second observing run and finished the year-long third observing run. Understanding, accounting, and/or compensating for the complex-valued response of each part of the upgraded detectors improves the overall accuracy of the estimated detector response to gravitational waves. We describe improved understanding and methods used to quantify the response of each detector, with a dedicated effort to define all places where systematic error plays a role. We use the detectors as they stand in the first half (six months) of the third observing run to demonstrate how each identified systematic error impacts the estimated strain and constrain the statistical uncertainty therein. For this time period, we estimate the upper limit on systematic error and associated uncertainty to be <7% in magnitude and <4 deg in phase (68% confidence interval) in the most sensitive frequency band 20-2000 Hz. The systematic error alone is estimated at levels of <2% in magnitude and <2 deg in phase.VB and EP acknowledge
the support of the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav),
Grant Number CE170100004. PBC acknowledges the support of the Spanish Agencia Estatal
de Investigaci´on and Ministerio de Ciencia, Innovaci´on y Universidades grants FPA2016-
76821-P the Vicepresidencia i Conselleria d’Innovaci´o, Recerca i Turisme del Govern de
les Illes Balears (Grant FPI-CAIB FPI/2134/2018), the Fons Social Europeu 2014–2020 de
les Illes Balears, the European Union FEDER funds, and the EU COST actions CA16104,
CA16214, CA17137 and CA18108. The authors would like to thank all of the essential
workers who put their health at risk during the COVID-19 pandemic, without whom we
would not have been able to complete this work. This paper carries LIGO Document Number
LIGO–P1900245
Characterization of systematic error in Advanced LIGO calibration
The raw outputs of the detectors within the Advanced Laser Interferometer
Gravitational-Wave Observatory need to be calibrated in order to produce the
estimate of the dimensionless strain used for astrophysical analyses. The two
detectors have been upgraded since the second observing run and finished the
year-long third observing run. Understanding, accounting, and/or compensating
for the complex-valued response of each part of the upgraded detectors improves
the overall accuracy of the estimated detector response to gravitational waves.
We describe improved understanding and methods used to quantify the response of
each detector, with a dedicated effort to define all places where systematic
error plays a role. We use the detectors as they stand in the first half (six
months) of the third observing run to demonstrate how each identified
systematic error impacts the estimated strain and constrain the statistical
uncertainty therein. For this time period, we estimate the upper limit on
systematic error and associated uncertainty to be in magnitude and deg in phase ( confidence interval) in the most sensitive frequency
band 20-2000 Hz. The systematic error alone is estimated at levels of
in magnitude and deg in phase
Frequency-domain fibre optic pressure sensors for Geophysical applications
This thesis presents methods for optical frequency-domain sensing of the strain on a fibre for use in a range of geophysical purposes. The Long Period Fibre Grating is modelled in detail to ascertain its viability as a hydrophone instrument, requiring very high sensitivity. Uncertainty analysis of such gratings illustrates that this will be difficult with available fibres. Other configurations such as down-hole pressure sensors are possible for these gratings, and several other sensing mechanisms
Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo
International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo
Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software