Moment actuator for correcting low-order aberrations of deformable mirrors

We propose a new moment actuator for correcting low-order aberrations of deformable mirrors (DMs) in high power laser (HPL) applications. The aberrations of a large thin faceplate are caused by the residual stress after fabrication, thermal soak, temperature gradient, actuator's hysteresis and creep, and so forth. Flattening procedure is always required to compensate for the DM's low-order aberrations before adaptive optics operation, and it necessarily reduces the remaining stroke of the actuator. In this paper, we present 16 bending moment actuator added at the baseplate for independent correction of the DM's low-order aberration, and therefore exploit the full dynamic range of the inherent actuators for high-order compensation. The arrangement of the moment actuator is optimized by using a new theoretical influence function (IF). We propose a coupling coefficient for the moment actuator, which is the first to our knowledge, when calculating the weighted IF with a closed-form equation, and show the improved correlations with experiments. We verify the experimental performance of the bending moment actuator with our in-house DM having a 200-mm silicon carbide (SiC) faceplate developed for HPLs. The moment actuator can be used as a plug-and-play kit for additional tuning of most DMs, and can be applied for combined DMs having the woofer-tweeter in a single body, active mirror mounts for high precision lithographic optics, to name a few.