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

TL;DR

This paper demonstrates experimentally that cooling sapphire mirrors in a cryogenic gravitational wave detector reduces thermal fluctuations and enhances sensitivity in the 90-240 Hz frequency range, reaching a maximum sensitivity of 2.2×10⁻¹⁹ m/√Hz at 165 Hz.

Contribution

First experimental reduction of mirror thermal fluctuations in a cryogenic GW detector using sapphire mirrors at 17-18 K, improving sensitivity.

Findings

Thermal fluctuation reduction observed at cryogenic temperatures.

Sensitivity improved in the 90-240 Hz frequency range.

Maximum sensitivity achieved at 165 Hz.

Abstract

The thermal fluctuation of mirror surfaces is the fundamental limitation for interferometric gravitational wave (GW) detectors. Here, we experimentally demonstrate for the first time a reduction in a mirror's thermal fluctuation in a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer Observatory at 17\,K and 18\,K. The detector sensitivity, which was limited by the mirror's thermal fluctuation at room temperature, was improved in the frequency range of 90\,Hz to 240\,Hz by cooling the mirrors. The improved sensitivity reached a maximum of $2.2 \times 10^{-19}\,\textrm{m}/\sqrt{\textrm{Hz}}$ at 165\,Hz.