Optical contamination control in the Advanced LIGO ultra-high vacuum system
Fused silica optics in the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors are extremely sensitive to optical scattering and absorption losses induced by both particulate and hydrocarbon contamination. At full power, the optical surfaces are illuminated with up to 200 kW/cm^2. Additionally, the round-trip test mass cavity loss budget is limited to 70 ppm total from all sources. Even low-level contaminants can result in laser damage to optics during the operation the interferometers, and/or the unacceptable reduction of overall detector sensitivity. These risks are mitigated by a two-pronged approach: quantifying contamination sources and the extent of contamination, then reducing sources and cleaning optics in-situ. As a result of these ongoing efforts, we now have a better understanding of what the contamination levels and sources are, and have made significant improvements to methods of controlling contamination, thus protecting the optics from losses and laser damage in the Advanced LIGO Interferometers.
© 2013 Society of Photo-Optical Instrumentation Engineers. The authors gratefully acknowledge the support of the United States National Science Foundation (award No. PHY-0757058). 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 PHY-0107417. Caltech also acknowledges financial support from the Science and Technology Facilities Council of the United Kingdom. This paper filed internally under LIGO document number LIGO-P1300192. LIGO Internal Reports may be accessed at https://dcc.ligo.org/cgi-bin/DocDB/DocumentDatabase. The authors wish to acknowledge the many colleagues in LIGO and the LIGO Scientific Collaboration who have supported this work. In particular, the authors are grateful for the guidance and support of Norna Robertson, Eric Gustafson, Garilynn Billingsley, and Dennis Coyne of LIGO Engineering at Caltech. The work would not have been possible without the outstanding efforts and collaboration of the installation teams at the LIGO observatories, particularly Matt Heintze at Livingston and Betsy Weaver at Hanford. In addition, the authors would like to thank industry contacts from the National Ignition Facility and Prudential Cleanroom Services, for their guidance and open collaboration.
Published - Phelps_2013p88852E.pdf