Description
The sensitivity of current gravitational-wave detectors such as LIGO and Virgo is limited by the optical power that can be sustained in their interferometer arms. Absorption of optical power in the main optics leads to mirror surface deformations, which in turn couple light into higher-order modes, resulting in degraded control sidebands, reduced squeezing enhancement, and the onset of parametric instabilities. The Einstein Telescope high-frequency (ET-HF) design aims to operate with 3 MW of circulating optical power—significantly higher than 350 kW that is achieved during LIGO’s O4 run.
To study and mitigate these thermal and optical effects, we are developing the ET-OPT facility, a high-power optical testbed to be built in the EMR region. The facility will feature a suspended optical cavity operating at similar peak intensities and g-factor to ET-HF. Using our real-time cavity spectroscopy technique, we will characterise mirror surface deformations as the cavity reaches thermal equilibrium and demonstrate that the optical mode basis can be stabilised and recovered.
In this poster, we introduce the principles of real-time cavity spectroscopy, outline the design of the ET-OPT facility, and discuss how these studies will inform the thermal and optical design of next-generation gravitational-wave detectors.
