Current status of the CLIO project

TL;DR

The CLIO project in Japan has advanced gravitational wave detection by demonstrating thermal-noise suppression through mirror cooling, achieving sensitivities comparable to LIGO at a fraction of the baseline length.

Contribution

This paper reports on the progress of the CLIO cryogenic gravitational wave detector, including sensitivity improvements and successful mirror cooling experiments.

Findings

Achieved a sensitivity of ~6 x 10^{-21}/√Hz at 400 Hz at room temperature.

Confirmed mirrors were cooled to 14 K in cryogenic experiments.

Observed noise reduction in aluminum wire suspensions when cooled.

Abstract

CLIO (Cryogenic Laser Interferometer Observatory) is a Japanese gravitational wave detector project. One of the main purposes of CLIO is to demonstrate thermal-noise suppression by cooling mirrors for a future Japanese project, LCGT (Large-scale Cryogenic Gravitational Telescope). The CLIO site is in Kamioka mine, as is LCGT. The progress of CLIO between 2005 and 2007 (room- and cryogenic-temperature experiments) is introduced in this article. In a room-temperature experiment, we made efforts to improve the sensitivity. The current best sensitivity at 300 K is about $6 \times 10^{-21} /\sqrt{\rm Hz}$ around 400 Hz. Below 20 Hz, the strain (not displacement) sensitivity is comparable to that of LIGO, although the baselines of CLIO are 40-times shorter (CLIO: 100m, LIGO: 4km). This is because seismic noise is extremely small in Kamioka mine. We operated the interferometer at room temperature for gravitational wave observations. We obtained 86 hours of data. In the cryogenic experiment, it was confirmed that the mirrors were sufficiently cooled (14 K). However, we found that the radiation shield ducts transferred 300K radiation into the cryostat more effectively than we had expected. We observed that noise caused by pure aluminum wires to suspend a mirror was suppressed by cooling the mirror.