Evaporative coating systems for very large astronomical mirrors

Barry A. Sabol, Bruce Atwood, J. M. Hill, J. T. Williams, Michael P. Lesser, Paul L. Byard, Warren B. Davison

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

4 Scopus citations

Abstract

The design of aluminization systems for the MMT Conversion 6.5 m mirror and the Columbus Project 8 m mirror has led us to reconsider many of the design issues and tradeoffs for such systems. Coating of the large honeycomb mirrors will be done in situ on the telescope with a portable bell jar forming the front half of a two-stage vacuum system. The mirror cell forms a 'dirty' vacuum behind the mirror to eliminate excess force on the glass. A multi-ring source geometry has been proposed to allow a 1.0 m spacing between the mirror surface and the sources thereby minimizing the size of the vacuum chamber. Evaporation source models have been developed to optimize the number of sources, ring spacing, and high incidence angle emission to achieve better than 5% rms deviation in coating thickness over the diameter. Code results are compared to empirical thickness profiles measured at the University of Arizona's (UA) Sunnyside 2.0 m coating facility. Cryoadsorption pumps are considered for reasons of economy, quality of vacuum, pumping speed, and reliability. The interaction of the cryopumps and getter pumping with the pumping/cleaning/deposition cycle is studied. Glow discharge cleaning is discussed and the results of deposition tests in 10-4 Torr residual argon are given. Electrical requirements are estimated and a novel tranformer design may decrease the current entering the chamber from 12,000 A to less than 600 A.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
EditorsLawrence D. Barr
PublisherPubl by Int Soc for Optical Engineering
Pages940-951
Number of pages12
ISBN (Print)081940280X
StatePublished - Dec 1 1990
EventAdvanced Technology Optical Telescopes IV - Tuscon, AZ, USA
Duration: Feb 12 1990Feb 16 1990

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume1236 pt 2
ISSN (Print)0277-786X

Other

OtherAdvanced Technology Optical Telescopes IV
CityTuscon, AZ, USA
Period2/12/902/16/90

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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  • Cite this

    Sabol, B. A., Atwood, B., Hill, J. M., Williams, J. T., Lesser, M. P., Byard, P. L., & Davison, W. B. (1990). Evaporative coating systems for very large astronomical mirrors. In L. D. Barr (Ed.), Proceedings of SPIE - The International Society for Optical Engineering (pp. 940-951). (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 1236 pt 2). Publ by Int Soc for Optical Engineering.