Comparison of arm cavity optical losses for the two wavelengths of the Einstein Telescope gravitational wave detector

TL;DR

This study compares optical losses at 1064 nm and 1550 nm for Einstein Telescope mirrors, finding that losses at 1064 nm are roughly twice as high, impacting future gravitational wave detector sensitivity.

Contribution

The paper provides experimental measurements and simulations of optical losses at two wavelengths, informing the design of next-generation gravitational wave detectors.

Findings

Optical losses at 1064 nm are about twice those at 1550 nm.

Measured absorption and scattering vary between the two wavelengths.

Simulations confirm the loss differences impact detector sensitivity.

Abstract

A new generation of gravitational wave detectors is currently being designed with the likely use of a different laser wavelength compared to current instruments. The estimation of the optical losses for this new wavelength is particularly relevant to derive the detector sensitivity and also to anticipate the optical performances of future instruments. In this article, we measured the absorption and angle-resolved scattering of several mirror samples in order to compare optical losses at a wavelength of 1064 and 1550\ nm. In addition, we have carried out simulations of the Einstein Telescope arm cavities at 1064 and 1550\ nm taking into account losses due to surface low-spatial frequency flatness. Our results suggest that optical losses as measured at 1064\ nm are about twice as large as those at 1550\ nm as predicted with a simple model.