Masatake Ohashi

Measurement of the mechanical loss of a cooled reflective coating for gravitational wave detection

We have measured the mechanical loss of a dielectric multilayer reflective coating (ion-beam sputtered

Present status of large-scale cryogenic gravitational wave telescope

{\mathrm{SiO}}_{2}

Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector.

and

The CLIO project

{\mathrm{Ta}}_{2}{\mathrm{O}}_{5}

Status of Japanese gravitational wave detectors

) in cooled mirrors. The loss was nearly independent of the temperature (

Japanese large-scale interferometers

4\text{ }\text{ }\mathrm{K}\ensuremath{\sim}300\text{ }\text{ }\mathrm{K}

Thermal lensing in cryogenic sapphire substrates

), frequency, optical loss, and stress caused by the coating, and the details of the manufacturing processes. The loss angle was

Status of the CLIO project

(4\ensuremath{\sim}6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}

Optical mode cleaner with suspended mirrors

. The temperature independence of this loss implies that the amplitude of the coating thermal noise, which is a severe limit in any precise measurement, is proportional to the square root of the temperature. Sapphire mirrors at 20 K satisfy the requirement concerning the thermal noise of even future interferometric gravitational wave detector projects on the ground, for example, LCGT.

Design and construction status of CLIO

The large-scale cryogenic gravitational wave telescope (LCGT) is the future project of the Japanese gravitational wave group. Two sets of 3 km arm length laser interferometric gravitational wave detectors will be built in a tunnel of Kamioka mine in Japan. LCGT will detect chirp waves from binary neutron star coalescence at 240 Mpc away with a S/N of 10. The expected number of detectable events in a year is two or three. To achieve the required sensitivity, several advanced techniques will be employed such as a low-frequency vibration-isolation system, a suspension point interferometer, cryogenic mirrors, a resonant side band extraction method, a high-power laser system and so on. We hope that the beginning of the project will be in 2005 and the observations will start in 2009.