LIGO Document G1301118-v4

Scattered Light Measurements for Advanced LIGO's Output Mode-Cleaner Mirrors

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The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), with sites in Livingston LA and Hanford WA, and its international partners, Virgo, GEO600, and KAGRA, are being built to detect gravitational waves, a phenomenon theorized by Einstein in his Theory of General Relativity (GR). A direct prediction of GR, gravitational waves are ripples in space-time that propagate at the speed of light and are created by violent astrophysical processes. The gravitational-wave detectors are all based on the Michelson interferometer, which has an input laser, a beam splitter, and two perpendicular arms with mirrors at each end. However, their configurations have significantly more complexity to augment the sensitivity. Higher order spatial modes can create 'junk light' that decreases the shot-noise limited sensitivity of the detectors. To combat this, each LIGO detector has an Output Mode-Cleaner (OMC) at its detection 'dark port'. Scattered light from the OMC mirrors can reduce the shot-noise limited sensitivity of the instruments, and add noise via stray and counter-propagating light. Thus it is important that the light scattering from the OMC mirrors in Advanced LIGO be minimal. This poster will describe measurements of the scattered light from sample Advanced LIGO OMC mirrors. 
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