Thermal-noise-limited underground interferometer CLIO

TL;DR

CLIO is a prototype underground cryogenic interferometer demonstrating reduced thermal noise with cooled sapphire mirrors, achieving thermal-noise-limited sensitivity at room temperature in a quiet underground environment.

Contribution

This paper reports the successful implementation of thermal noise reduction techniques and the achievement of thermal-noise-limited sensitivity in an underground cryogenic interferometer.

Findings

Achieved thermal-noise-limited sensitivity at room temperature.

Eliminated thermal noise from conductive coil-holders.

Verified advantages of underground location for gravitational wave detection.

Abstract

We report on the current status of CLIO (Cryogenic Laser Interferometer Observatory), which is a prototype interferometer for LCGT (Large Scale Cryogenic Gravitational-Wave Telescope). LCGT is a Japanese next-generation interferometric gravitational wave detector featuring the use of cryogenic mirrors and a quiet underground site. The main purpose of CLIO is to demonstrate a reduction of the mirror thermal noise by cooling the sapphire mirrors. CLIO is located in an underground site of the Kamioka mine, 1000 m deep from the mountain top, to verify its advantages. After a few years of commissioning work, we have achieved a thermal-noise-limited sensitivity at room temperature. One of the main results of noise hunting was the elimination of thermal noise caused by a conductive coil-holder coupled with a pendulum through magnets.