Feasibility study of beam-expanding telescopes in the interferometer arms for the Einstein Telescope

TL;DR

This paper explores the potential use of beam-expander telescopes in the Einstein Telescope's interferometer arms, demonstrating their feasibility and ability to optimize optical mode matching in the detector design.

Contribution

It presents a feasibility analysis and an example implementation of beam-expander telescopes in the Einstein Telescope, enhancing optical layout flexibility and mode matching capabilities.

Findings

Beam-expander telescopes can be integrated into the ET design.

Tuning beam-expander telescopes can compensate for mode mismatches.

The proposed implementation aligns with the 2020 ET design update.

Abstract

The optical design of the Einstein Telescope (ET) is based on a dual-recycled Michelson interferometer with Fabry-Perot cavities in the arms. ET will be constructed in a new infrastructure, allowing us to consider different technical implementations beyond the constraints of the current facilities. In this paper we investigate the feasibility of using beam-expander telescopes in the interferometer arms. We provide an example implementation that matches the optical layout as presented in the ET design update 2020. We further show that the beam-expander telescopes can be tuned to compensate for mode mismatches between the arm cavities and the rest of the interferometer.