Controlling Light Scatter in Advanced LIGO

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LIGO-T080064-x0
14 Mar 2008, 00:00

Abstract:: A significant issue in the Advance LIGO interferometer is the amount of scattered light. One purpose of the Auxiliary Optics Support (AOS) subsystem is to control and minimize the scattered light in the interferometer through the use of optical components such as baffles and beam dumps. Although these components significantly reduce scattered light, they also have inherent levels of scatter due to material composition and geometry. The light scatter from the AOS components can introduce noise into the LIGO detectors because they are not seismically isolated. In order to quantify the amount of scattered light and to qualify materials for use in AOS, we have constructed a highly sensitive scatterometer capable of measuring the Bidirectional Reflectance Distribution Function (BRDF) and the reflectivity of a material. We were able to verify the design concept of the scatterometer using a calibrated lambertian scattering surface. The materials of primary interest were black welder’s glass, a super polished Brewster window, Laser Black 3188, and several types of oxidized stainless steel. We were able to achieve the sensitivity necessary to measure the BRDF and reflectivity of all the materials of interest. The material with the lowest BRDF was black glass with a BRDF 10^-6

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LIGO Document T080064-v1