Demonstration of a robust curved carbon fiber reinforced polymer deformable mirror with low surface error

Carbon fiber reinforced polymer (CFRP) composites provide several advantages as a substrate for thin-shell adaptive secondary mirrors, including high stiffness-to-weight ratio and low coefficient of thermal expansion (CTE). We have addressed some of these concerns using a prototype CFRP mirror under actuation. Using 4D and Newton interferometry, we present measurements of surface quality at a range of temperatures. Under actuator relaxation at room temperature, its surface error is low (92 nm RMS) and dominated by edge curvature. This error is reduced further under best actuator correction to 43 nm RMS, placing it into consideration for use in near-IR astronomy. The low surface error internal to the outer ring of actuators - 17 nm RMS at 600F and 33 nm RMS at 200F - suggests that larger mirrors will have a similar figure quality under actuator correction on ground-based AO systems. Furthermore, the actuator forces required to correct the figure are small compared to the dynamic range of voice coil actuators (~0.1 N). In addition, surface roughness is characterized to address the effects of high spatial frequency errors.