Cryogenic Optical Scatter Measurement of Crystalline Silicon

Crystalline Silicon (cSi) is a candidate substrate for the test masses (main mirrors) of future cryogenically cooled gravitational wave detectors. To understand the achievable performance and required manufacturing requirements, this material's optical and thermal properties must be thoroughly explored. Light scattering from the test masses leads to optical loss and nonlinear noise that reduces the performance of gravitational wave detectors. In this poster we demonstrate techniques for determining the optical scattering of crystalline silicon versus temperature. We also present an alternative (to contact temperature sensors) method for determining the temperature of a crystalline silicon sample via an optical etalon.