Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope

S. C. West, James H Burge, B. Cuerden, W. Davison, J. Hagen, H. M. Martin, M. T. Tuell, C. Zhao, T. Zobrist

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

17 Citations (Scopus)

Abstract

The Giant Magellan Telescope has a 25 meter f/0.7 near-parabolic primary mirror constructed from seven 8.4 meter diameter segments. Several aspects of the interferometric optical test used to guide polishing of the six off-axis segments go beyond the demonstrated state of the art in optical testing. The null corrector is created from two obliquelyilluminated spherical mirrors combined with a computer-generated hologram (the measurement hologram). The larger mirror is 3.75 m in diameter and is supported at the top of a test tower, 23.5 m above the GMT segment. Its size rules out a direct validation of the wavefront produced by the null corrector. We can, however, use a reference hologram placed at an intermediate focus between the two spherical mirrors to measure the wavefront produced by the measurement hologram and the first mirror. This reference hologram is aligned to match the wavefront and thereby becomes the alignment reference for the rest of the system. The position and orientation of the reference hologram, the 3.75 m mirror and the GMT segment are measured with a dedicated laser tracker, leading to an alignment accuracy of about 100 microns over the 24 m dimensions of the test. In addition to the interferometer that measures the GMT segment, a separate interferometer at the center of curvature of the 3.75 m sphere monitors its figure simultaneously with the GMT measurement, allowing active correction and compensation for residual errors. We describe the details of the design, alignment, and use of this unique off-axis optical test.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
Volume7739
DOIs
StatePublished - 2010
EventModern Technologies in Space- and Ground-Based Telescopes and Instrumentation - San Diego, CA, United States
Duration: Jun 27 2010Jul 2 2010

Other

OtherModern Technologies in Space- and Ground-Based Telescopes and Instrumentation
CountryUnited States
CitySan Diego, CA
Period6/27/107/2/10

Fingerprint

Hologram
Holograms
Telescopes
Telescope
Mirror
Alignment
alignment
telescopes
mirrors
Mirrors
Wavefronts
Wave Front
Corrector
Interferometer
Interferometers
Null
interferometers
Optical testing
Optical Testing
Polishing

Keywords

  • Aspheres
  • Interferometry
  • Null lens
  • Optical alignment
  • Optical testing
  • Telescopes

ASJC Scopus subject areas

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

Cite this

West, S. C., Burge, J. H., Cuerden, B., Davison, W., Hagen, J., Martin, H. M., ... Zobrist, T. (2010). Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope. In Proceedings of SPIE - The International Society for Optical Engineering (Vol. 7739). [77390N] https://doi.org/10.1117/12.857251

Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope. / West, S. C.; Burge, James H; Cuerden, B.; Davison, W.; Hagen, J.; Martin, H. M.; Tuell, M. T.; Zhao, C.; Zobrist, T.

Proceedings of SPIE - The International Society for Optical Engineering. Vol. 7739 2010. 77390N.

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

West, SC, Burge, JH, Cuerden, B, Davison, W, Hagen, J, Martin, HM, Tuell, MT, Zhao, C & Zobrist, T 2010, Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope. in Proceedings of SPIE - The International Society for Optical Engineering. vol. 7739, 77390N, Modern Technologies in Space- and Ground-Based Telescopes and Instrumentation, San Diego, CA, United States, 6/27/10. https://doi.org/10.1117/12.857251
West SC, Burge JH, Cuerden B, Davison W, Hagen J, Martin HM et al. Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope. In Proceedings of SPIE - The International Society for Optical Engineering. Vol. 7739. 2010. 77390N https://doi.org/10.1117/12.857251
West, S. C. ; Burge, James H ; Cuerden, B. ; Davison, W. ; Hagen, J. ; Martin, H. M. ; Tuell, M. T. ; Zhao, C. ; Zobrist, T. / Alignment and use of the optical test for the 8.4 m off-axis primary mirrors of the Giant Magellan Telescope. Proceedings of SPIE - The International Society for Optical Engineering. Vol. 7739 2010.
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