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.
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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 Letter, we describe the first observation of parametric instability in a gravitational wave detector, and the means by which it has been removed as a barrier to progress.
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Abstract 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 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.
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The characterization of the Advanced LIGO detectors in the second and third observing runs has increased the sensitivity of the instruments, allowing for a higher number of detectable ...gravitational-wave signals, and provided confirmation of all observed gravitational-wave events. In this work, we present the methods used to characterize the LIGO detectors and curate the publicly available datasets, including the LIGO strain data and data quality products. We describe the essential role of these datasets in LIGO–Virgo Collaboration analyses of gravitational-waves from both transient and persistent sources and include details on the provenance of these datasets in order to support analyses of LIGO data by the broader community. Finally, we explain anticipated changes in the role of detector characterization and current efforts to prepare for the high rate of gravitational-wave alerts and events in future observing runs.
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 high-power 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.
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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's 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.
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