Measurement of large convex aspheres

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

45 Scopus citations

Abstract

Large convex aspheres are notoriously difficult to fabricate because of the tremendous cost and difficulty of making accurate measurements of the optical surfaces. The new 6.5- and 8-m-class telescopes require convex secondary mirrors that are larger, more aspheric, and more accurately figured than those for existing telescopes. Two powerful measurement techniques have been implemented at the Mirror Lab and demonstrated to be accurate and economical. The polished surfaces are interferometrically measured using holographic test plates. This measurement technique uses full-aperture test plates with computer-generated holograms (CGH) fabricated onto spherical reference surfaces. When supported a few millimeters from the secondary and properly illuminated with laser light, an interference pattern is formed that shows the secondary surface errors. The hologram consists of annular rings of metal drawn onto the curved test plate surface using a custom-built writing machine. This test has been implemented for secondaries up to 1.15-m diameter, with 4 nm rms surface measurement accuracy. In addition to this test, a swing arm profilometer was built to measure the rough surface during aspherization and loose abrasive grinding. The machine uses simple motions and high quality components to achieve 50 nm rms measurement accuracy over 1.8-m mirrors.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSociety of Photo-Optical Instrumentation Engineers
Pages362-373
Number of pages12
ISBN (Print)0819422681
StatePublished - Dec 1 1997
EventOptical Telescopes of Today and Tomorrow - Landskrona/Hven, Swed
Duration: May 29 1996May 29 1996

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume2871
ISSN (Print)0277-786X

Other

OtherOptical Telescopes of Today and Tomorrow
CityLandskrona/Hven, Swed
Period5/29/965/29/96

ASJC Scopus subject areas

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

Fingerprint Dive into the research topics of 'Measurement of large convex aspheres'. Together they form a unique fingerprint.

  • Cite this

    Burge, J. H. (1997). Measurement of large convex aspheres. In Proceedings of SPIE - The International Society for Optical Engineering (pp. 362-373). (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 2871). Society of Photo-Optical Instrumentation Engineers.