Calibration and test procedures for the NFIRAOS deformable mirror prototypes

Abstract

A test setup and detailed plan for safe characterization of prototype deformable mirrors (DMs) for the Thirty Meter Telescope' s Narrow Field Infrared Adaptive Optics System (NFIRAOS) are presented. The DM size and performance requirements for NFIRAOS are such that prototypes must be built and tested before commissioning the final deliverables in order to mitigate risk. There are two prototypes under test; the actuators have been constructed with the pitch, size and stroke range specified for the full scale DMs, and on the order of 15% of the total number of actuators required by DM0, the ground-conjugated DM. The diameters of the active areas of the prototypes are approximately 35% of the full DM0 diameter. The performance in terms of stroke, linearity, hysteresis and overall controllability must meet requirements at room temperature and at -30 degrees Celsius. NRC HAA has implemented a test setup to characterize the performance of the DM prototypes in this thermal environment. A testing procedure has also been developed to verify the technology up to its limits, while protecting from damage. A primary risk of damage comes from excessive inter-actuator stroke which must be carefully controlled, particularly in the case of non-linear and hysteretic actuators. A detailed calibration procedure and actuator protection scheme has been developed.