Optical performance of large-area crystalline coatings

Given their excellent optical and mechanical properties, substrate-transferred crystalline coatings are an exciting alternative to amorphous multilayers for applications in precision interferometry. The high mechanical quality factor of these single-crystal interference coatings reduces the limiting thermal noise in precision optical instruments such as reference cavities for narrow-linewidth laser systems and interferometric gravitational wave detectors. In this manuscript, we explore the optical performance of GaAs/AlGaAs crystalline coatings transferred to 50.8-mm (2-inch) diameter fused silica and sapphire substrates. We present results for the transmission, scattering, absorption, and surface quality of these prototype samples including the defect density and micro-roughness. These novel coatings exhibit optical performance on par with state-of-the-art dielectric structures, encouraging further work focused on the fabrication of larger optics using this technique. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement