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

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