System for precise temperature sensing and thermal control of borosilicate honeycomb mirrors during polishing and testing

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

5 Scopus citations

Abstract

A 1.8 m f/1 borosilicate honeycomb primary for the Vatican Advanced Technology Telescope (VATT) is being polished at the Steward Observatory Mirror Laboratory. To reduce thermal distortion of large borosilicate honeycomb telescope mirrors to a negligible level during polishing, the glass must be maintained isothermal to within 0.1 °C. It is also essential to minimize temperature variations in the air while a test is in progress. Testing of the surface is done in air using a laser and interferometer mounted above the mirror. To control refractive index variation in the light path of the laser, assuming some turbulence, the air is required to be isothermal to 0.2 °C. A system designed to achieve these goals has been installed in the Mirror Laboratory. Thermocouples are employed as temperature sensors in the polishing room, air ducts, and on the mirror itself. The output of each thermocouple is referred to one of two isothermal blocks of aluminum. By repeated reading, measurements are made to an accuracy of 0.005 °C at a rate of one thermocouple per second. Thermal control of the mirror is achieved by blowing air of controlled temperature into each cell of the honeycomb structure. Preliminary results presented here show that the new system is easily capable of keeping the glass within the 0.1 °C peak-to-valley limit, while maintaining adequate control of the thermal environment in the polishing room. A similar system will be used in polishing the next generation of large telescope primaries to be cast by Steward Observatory in the 1990s, and the system's temperature tracking capability makes it ideal for use in a telescope on-site to improve seeing.

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
Pages844-852
Number of pages9
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

    Lloyd-Hart, M. (1990). System for precise temperature sensing and thermal control of borosilicate honeycomb mirrors during polishing and testing. In L. D. Barr (Ed.), Proceedings of SPIE - The International Society for Optical Engineering (pp. 844-852). (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 1236 pt 2). Publ by Int Soc for Optical Engineering.