The Optical Engineering and Fabrication Facility (OEFF) at the College of Optical Sciences, University of Arizona has successfully fabricated a 6.5m primary mirror and conducted integration and testing (I & T) of the primary mirror and telescope cell assembly for the University of Tokyo Atacama Observatory. The mirror has been fabricated using a new facility and advanced technologies developed by the group, including fabrication process optimization, a super-stable optical metrology support, infrared and visible metrology with high accuracy, and interferometry. Fabrication process optimization has simulated the entire fabrication process from the initial grinding to final polishing to specification, and optimized the tooling, frequency of metrology, and estimated convergence. Through the project the new process optimization successfully demonstrated the performance and guided the process in a deterministic way.
The 6.5m primary mirror is made of E6 bolo-silicate glass with a honeycomb structure. Due to the scale it requires a mechanically and thermally stable metrology support to ensure highly accurate metrology. The new metrology support has demonstrated its extremely stable force stability and thermal stability over the project period.
Metrology of large optics is always a challenge and the OEFF group has made outstanding advancement in IR and visible metrology and applied them seamlessly during the mirror fabrication with extremely low uncertainty.
By applying the newly developed facility and technologies, the OEFF group successfully fabricated the 6.5m primary mirror in less than 7months, which is about 3 times faster than past 6.5m mirror fabrication at UA.
After fabrication the mirror was integrated to the telescope cell and the primary mirror cell assembly has been tested using optical metrology to identify the static and dynamic behavior of the system. The testing includes support actuator influence functions, the nominal support force set, bending mode correction, and assessment of deliverable image quality.
This paper presents the technical aspects of the mirror fabrication, advancement of metrology and I & T of the 6.5m primary mirror assembly.