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.
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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