Sapphire mirror for the KAGRA gravitational wave detector
KAGRA, the Japanese interferometric gravitational wave detector currently under construction, will employ sapphire test masses for its cryogenic operation. Sapphire has an advantage in its higher thermal conductivity near the operating temperature 20 K compared to fused silica used in other gravitational wave detectors, but there are some uncertain properties for the application such as hardness, optical absorption, and birefringence. We introduce an optical design of the test masses and our recent R&D results to address the above properties. Test polish of sapphire substrate has especially proven that specifications on the surface are sufficiently met. Recent measurements of absorption and inhomogeneity of the refractive index of the sapphire substrate indicate that the other properties are also acceptable to use sapphire crystal as test masses.
© 2014 American Physical Society. Published 24 March 2014; Received 3 February 2014. We are grateful for financial support from the Leading-edge Research Infrastructure Program funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan. The LIGO Observatories were constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the NSF under cooperative agreement No. PHY- 9210038. The LIGO Laboratory operates under cooperative agreement No. PHY-0328418. We thank our colleagues in both the KAGRA Collaboration and the LIGO Scientific Collaboration (LSC). This paper has document numbers JGW-P1302017 and LIGO-P1400005.
Published - PhysRevD.89.062003.pdf