The fabrication of TMT’s primary mirror segments at Coherent Inc. in California continues to progress well. To date, a total of 19 M1 polished roundels have been delivered to TMT’s secure warehouse facility for storage.
Each roundel is being produced in accordance to strict technical specifications, and meeting these requirements is critical to the success of the TMT Observatory. To ensure that each segment will perform satisfactorily, optical interferometers are used to closely analyze and control the roundels, and to verify the quality of their polished surfaces. All interferometric metrology data from Coherent were reviewed using independent analysis at NASA's Jet Propulsion Laboratory (JPL), which is partnering with TMT. A variety of analyses successfully met JPL’s chart of performance metrics. The surface measurement table from Coherent met and even exceeded the TMT’s expectations.
“Indeed, we are thrilled and confident about the roundels’ quality,” says Glen Cole, TMT lead Optical Fabrication engineer, while visiting the Coherent production facility in the Bay area last December. “Being out there and looking directly at the improvements made to optimize the efficiency of all processes is very impressive.”
In addition to inspecting the delivered roundels, Cole was also co-training at an extended coaching session provided for the India TMT Coordination Centre’s (ITCC) optical engineers.
As soon as Covid-19 travel restrictions were lifted, two TMT India engineers flew to California for a training on producing TMT’s aspherical polished roundels using the Stress Mirror Polishing technology. During this instructional phase, which is taking place independently of Coherent’s mirror production, Coherent engineers are providing hands-on coaching sessions on the operations of the specific tools and equipment that ITCC engineers will use in their newly built India-TMT Optics Fabrication Facility (ITOFF)1. The coaching also includes instruction on the qualification tests performed during roundel production. In the coming months, a third person will come from India for a second phase of training.
“Coherent is honored to host our guests from India and share our expertise in Stress Mirror Polishing technology,” says Lou Marchetti, Development Engineer at Coherent leading the polishing training effort. “We look forward to having that team join us in polishing these mirrors to perfection.”
1 https://www.tmt.org/news/479 “Inauguration of the ITOFF facility, CREST Campus, IIA, India”, January 20th, 2021