Manufacture and final tests of the LSST monolithic primary/tertiary mirror

H. M. Martin, J. R.P. Angel, G. Z. Angeli, J. H. Burge, W. Gressler, D. W. Kim, J. S. Kingsley, K. Law, M. Liang, D. Neill, J. Sebag, P. A. Strittmatter, M. T. Tuell, S. C. West, N. J. Woolf, B. Xin

Research output: Chapter in Book/Report/Conference proceedingConference contribution

13 Scopus citations


The LSST M1/M3 combines an 8.4 m primary mirror and a 5.1 m tertiary mirror on one glass substrate. The combined mirror was completed at the Richard F. Caris Mirror Lab at the University of Arizona in October 2014. Interferometric measurements show that both mirrors have surface accuracy better than 20 nm rms over their clear apertures, in nearsimultaneous tests, and that both mirrors meet their stringent structure function specifications. Acceptance tests showed that the radii of curvature, conic constants, and alignment of the 2 optical axes are within the specified tolerances. The mirror figures are obtained by combining the lab measurements with a model of the telescope's active optics system that uses the 156 support actuators to bend the glass substrate. This correction affects both mirror surfaces simultaneously. We showed that both mirrors have excellent figures and meet their specifications with a single bending of the substrate and correction forces that are well within the allowed magnitude. The interferometers do not resolve some small surface features with high slope errors. We used a new instrument based on deflectometry to measure many of these features with sub-millimeter spatial resolution, and nanometer accuracy for small features, over 12.5 cm apertures. Mirror Lab and LSST staff created synthetic models of both mirrors by combining the interferometric maps and the small highresolution maps, and used these to show the impact of the small features on images is acceptably small.

Original languageEnglish (US)
Title of host publicationAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation II
EditorsRamon Navarro, James H. Burge
ISBN (Electronic)9781510602038
StatePublished - 2016
EventAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation II - Edinburgh, United Kingdom
Duration: Jun 26 2016Jul 1 2016

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation II
Country/TerritoryUnited Kingdom


  • Active optics
  • Aspheres
  • LSST
  • Optical fabrication
  • Optical testing
  • Telescopes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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