The CLIO project

The CLIO project including a 100 m baseline cryogenic gravitational wave laser interferometer and a 100 m baseline geophysical strain meter was conducted in the Kamioka mine in Japan to investigate the technical feasibility of the large-scale cryogenic gravitational wave telescope (LCGT), which is planned to be constructed in the same Kamioka mine with 30 times longer baseline than CLIO, and to demonstrate the collaborative operation between these instruments about long-term continuous operation and gravitational wave signal veto analysis. About the cryogenic gravitational wave interferometer, the whole vacuum system and four cryostats, which house and cool sapphire mirrors, were constructed, and the required vacuum level of 10 −6 mbar and the temperature of 8 K at the inner radiation shield in the cryostat were achieved. About the geophysical strain meter, the obtained geophysical strain in the Kamioka mine was successfully simulated with a finite element model with a good agreement with less than 5% error. The strain meter also verified a permanent ground step change of micrometre order due to some earthquakes. We present the recent progress about the CLIO project.