29 research outputs found
Performance Characterization of the Dual-Recycled Michelson Subsystem in Advanced LIGO
General relativity predicts the existence of gravitational waves as ripples in spacetime propagating at the speed of light. They couple to matter weakly, which implies only cataclysmic cosmic events generating such waves can be detected. Binary neutron star coalescences are, for example, one of the most promising detectable source. Their weak coupling also implies that very sensitive instruments are needed to detect them, and the most sensitive so far have been laser interferometers with km-scale arms. The Laser Interferometric Gravitational wave Observatory (LIGO) is exactly such an instrument, and the most sensitive in the world to the date of this dissertation. It operates two identical interferometers, one in Hanford, WA and one in Livingston, LA. I will present noise studies on two different topics.First, studies of environmental effects in the enhanced LIGO detector era (2008-2010) for both sites, showing that stationary ambient environmental noise did not limit the sensitivity at the time. After enhanced LIGO, advanced LIGO began installation, where all hardware was replaced except the enclosing vacuum system. The expected improvement in sensitivity is designed to be tenfold, which results in a factor of a thousand in the volume of space from where a source could be detected. This dissertation then focuses on a sub-configuration of advanced LIGO, the dual-recycled Michelson interferometer (DRMI), which is the LIGO instrument without the 4km arms. I will expose in detail the length sensing and control scheme which is the cornerstone of LIGO\u27s ability to provide a linear gravitational wave readout. We model the behavior of the instrument in order to identify key commissioning targets. I will present models and measurements I performed at the Livingston Observatory for assessing two main topics: the sensing performance and the noise couplings in the DRMI. This work has only been possible with the support from the NSF grants NSF-PHY 0905184 and 1205882
Correlated noise in networks of gravitational-wave detectors: subtraction and mitigation
One of the key science goals of advanced gravitational-wave detectors is to
observe a stochastic gravitational-wave background. However, recent work
demonstrates that correlated magnetic fields from Schumann resonances can
produce correlated strain noise over global distances, potentially limiting the
sensitivity of stochastic background searches with advanced detectors. In this
paper, we estimate the correlated noise budget for the worldwide Advanced LIGO
network and conclude that correlated noise may affect upcoming measurements. We
investigate the possibility of a Wiener filtering scheme to subtract correlated
noise from Advanced LIGO searches, and estimate the required specifications. We
also consider the possibility that residual correlated noise remains following
subtraction, and we devise an optimal strategy for measuring astronomical
parameters in the presence of correlated noise. Using this new formalism, we
estimate the loss of sensitivity for a broadband, isotropic stochastic
background search using 1 yr of LIGO data at design sensitivity. Given our
current noise budget, the uncertainty with which LIGO can estimate energy
density will likely increase by a factor of ~4--if it is impossible to achieve
significant subtraction. Additionally, narrowband cross-correlation searches
may be severely affected at low frequencies f < 45 Hz without effective
subtraction.Comment: 16 pages, 8 figure
Noise in the LIGO Livingston Gravitational Wave Observatory due to Trains
Environmental seismic disturbances limit the sensitivity of LIGO
gravitational wave detectors. Trains near the LIGO Livingston detector produce
low frequency (0.5-10 Hz) ground noise that couples into the gravitational wave
sensitive frequency band (10-100 Hz) through light reflected in mirrors and
other surfaces. We investigate the effect of trains during the Advanced LIGO
third observing run, and propose a method to search for narrow band seismic
frequencies responsible for contributing to increases in scattered light.
Through the use of the linear regression tool Lasso (least absolute shrinkage
and selection operator) and glitch correlations, we identify the most common
seismic frequencies that correlate with increases in detector noise as 0.6-0.8
Hz, 1.7-1.9 Hz, 1.8-2.0 Hz, and 2.3-2.5 Hz in the LIGO Livingston corner
station.Comment: 18 pages (including bibliography), 17 figures, 2 tables, and 1
appendix. Submitted to Classical and Quantum Gravit
Modeling and Reduction of High Frequency Scatter Noise at LIGO Livingston
The sensitivity of aLIGO detectors is adversely affected by the presence of
noise caused by light scattering. Low frequency seismic disturbances can create
higher frequency scattering noise adversely impacting the frequency band in
which we detect gravitational waves. In this paper, we analyze instances of a
type of scattered light noise we call "Fast Scatter" that is produced by motion
at frequencies greater than 1 Hz, to locate surfaces in the detector that may
be responsible for the noise. We model the phase noise to better understand the
relationship between increases in seismic noise near the site and the resulting
Fast Scatter observed. We find that mechanical damping of the Arm Cavity
Baffles (ACBs) led to a significant reduction of this noise in recent data. For
a similar degree of seismic motion in the 1-3 Hz range, the rate of noise
transients is reduced by a factor of ~ 50.Comment: 23 pages, 19 figure
Point Absorber Limits to Future Gravitational-Wave Detectors
High-quality optical resonant cavities require low optical loss, typically on the scale of parts per million. However, unintended micron-scale contaminants on the resonator mirrors that absorb the light circulating in the cavity can deform the surface thermoelastically, and thus increase losses by scattering light out of the resonant mode. The point absorber effect is a limiting factor in some highpower cavity experiments, for example, the Advanced LIGO gravitational wave detector. In this Letter, we present a general approach to the point absorber effect from first principles and simulate its contribution to the increased scattering. The achievable circulating power in current and future gravitational-wave detectors is calculated statistically given different point absorber configurations. Our formulation is further confirmed experimentally in comparison with the scattered power in the arm cavity of Advanced LIGO measured by in-situ photodiodes. The understanding presented here provides an important tool in the global effort to design future gravitational wave detectors that support high optical power, and thus reduce quantum noise
Observation of Parametric Instability in Advanced LIGO
Parametric instabilities have long been studied as a potentially limiting
effect in high-power interferometric gravitational wave detectors. Until now,
however, these instabilities have never been observed in a kilometer-scale
interferometer. In this work we describe the first observation of parametric
instability in an Advanced LIGO detector, and the means by which it has been
removed as a barrier to progress
The Advanced LIGO Input Optics
The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015. These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves. The input optics play a significant part in allowing these devices to reach such sensitivities. Residing between the pre-stabilized laser and the main interferometer, the input optics subsystem is tasked with preparing the laser beam for interferometry at the sub-attometer level while operating at continuous wave input power levels ranging from 100 mW to 150 W. These extreme operating conditions required every major component to be custom designed. These designs draw heavily on the experience and understanding gained during the operation of Initial LIGO and Enhanced LIGO. In this article, we report on how the components of the input optics were designed to meet their stringent requirements and present measurements showing how well they have lived up to their design
Measurement and subtraction of Schumann resonances at gravitational-wave interferometers
Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible
The advanced LIGO input optics
The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015. These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves. The input optics play a significant part in allowing these devices to reach such sensitivities. Residing between the pre-stabilized laser and the main interferometer, the input optics subsystem is tasked with preparing the laser beam for interferometry at the sub-attometer level while operating at continuous wave input power levels ranging from 100 mW to 150 W. These extreme operating conditions required every major component to be custom designed. These designs draw heavily on the experience and understanding gained during the operation of Initial LIGO and Enhanced LIGO. In this article, we report on how the components of the input optics were designed to meet their stringent requirements and present measurements showing how well they have lived up to their design