Crystalline coatings for near-IR ring laser gyroscopes

Substrate-transferred crystalline coatings represent an entirely new concept in high-performance optical coatings. This technology was originally developed as a solution to the long-standing thermal noise limitation found in ultrastable optical interferometers, impacting cavity-stabilized laser systems for precision spectroscopy and optical atomic clocks, as well as interferometric gravitational wave (GW) detectors [1]. The ultimate stability of these systems is currently dictated by coating Brownian noise, driven by the excess mechanical losses of the materials that comprise the highly reflective elements of the cavity end mirrors. Compared with state-of-the art ion-beam sputtered dielectric reflectors, crystalline coatings, comprising substrate-transferred GaAs/AlGaAs heterostructures, exhibit competitive reflectivity together with a significantly enhanced mechanical quality, resulting in a thermally-limited noise floor consistent with a tenfold reduction in mechanical damping at room temperature [2]. Building upon this initial demonstration, we have recently developed high-performance crystalline supermirrors with parts-per-million levels of optical losses, including both absorption and scatter, at wavelengths spanning 1000 to nearly 4000 nm, with experimentally verified absorption coefficients below 0.1 cm-1 in the near infrared [3]. These advancements have opened up additional application areas including the focus of this work. Here we demonstrate the first implementation of crystalline supermirrors in an active laser system, expanding the core application area of these low-thermal noise cavity end mirrors to inertial sensing systems and specifically next-generation high-sensitivity ring-laser gyroscopes [4,5].