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Challenges of Big Telescope Mirrors Draws a Crowd at OSA Optical Design and Fabrication Congress

OSA Communications

It was standing room only at a session on large optics manufacturing and testing during the OSA Optical Design and Fabrication Congress held 10-12 June 2019 at OSA headquarters in Washington, D.C.

Caption: Remi Bourgois of SAFRAN REOSC talks about his company's efforts to fabricate mirrors for the Extremely Large Telescope in Chile 

Credit: OSA Communications 

The challenges of fabricating and finishing large mirrors for optical telescopes were discussed by speakers including University of New Mexico’s Tony Hull who pointed out that the technology behind building large mirrors has evolved considerably from a time when 4 to 5 m mirrors were considered “large,” followed by 6 to 8 m mirrors up to today when 20 m, 25 m and 30 m mirrors are being fabricated for the world’s most powerful telescopes.

Other speakers included Remi Bourgois of SAFRAN REOSC in France, which was awarded a contract in March to build the fifth and final mirror for the Extremely Large Telescope (ELT) in Chile. When completed, it will be the world’s largest mirror at 39 m. First light for the telescope is planned for 2025. Jim Burge of Arizona Optical Systems (AOS) discussed the use of computer-generated holograms (CGH) to accurately align large telescope mirrors. His company is working with Ball Aerospace to build the optical components for the Large Synoptic Survey Telescope (LSST). AOS will produce the large precision lenses required to focus sky images onto the largest CCD mosaic in the world. The company will design and build the calibration system that will be used to perform the final optical measurements of the LSST camera assembly lenses. Burge also described how AOS will use both interferometric metrology and CGH for fabrication of the Thirty Meter Telescope mirror. The TMT uses a primary mirror made from 492 1.4 -m segments with 82 different aspheric prescriptions. Each segment will be measured using Fizeau interferometry and CGH aspheric correction, Burge said. The large optics session overall highlighted the dawn of a dynamic new era for ground-based astronomical observatories in which optical sciences are delivering unprecedented abilities to see into deep space to answer fundamental questions about the history and nature of the universe.  

Image for keeping the session alive