Thermal modelling of Advanced LIGO test masses
High-reflectivity fused silica mirrors are at the epicentre of today's advanced gravitational wave detectors. In these detectors, the mirrors interact with high power laser beams. As a result of finite absorption in the high reflectivity coatings the mirrors suffer from a variety of thermal effects that impact on the detectors' performance. We propose a model of the Advanced LIGO mirrors that introduces an empirical term to account for the radiative heat transfer between the mirror and its surroundings. The mechanical mode frequency is used as a probe for the overall temperature of the mirror. The thermal transient after power build-up in the optical cavities is used to refine and test the model. The model provides a coating absorption estimate of 1.5–2.0 ppm and estimates that 0.3 to 1.3 ppm of the circulating light is scattered onto the ring heater.
© 2017 IOP Publishing Ltd. Received 9 December 2016, revised 14 April 2017. Accepted for publication 21 April 2017. Published 18 May 2017. This work is supported by the LSC fellows program and the Science and Technology Facilities Council (STFC). LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation, and operates under Cooperative Agreement No. PHY-0757058. Advanced LIGO was built under Grant No. PHY-0823459. The authors would like to thank Haixing Miao, Daniel Brown, and Anna Green for comments and suggestions. The authors also thank the LIGO Livingston Observatory staff for additional support.
Submitted - 1612.02866.pdf