Absolute calibration of null correctors using dual computer-generated holograms

Proteep C V Mallik, Rene Zehnder, James H Burge, Alexander Poleshchuk

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

6 Scopus citations

Abstract

There is an increasing need for precision large aspheric optics with small focal ratios for astronomical and space applications. However, testing such optics presents a challenge. Interferometric testing of aspheric surfaces often requires the use of null lenses. Many of these null lenses are tested using a certification computer-generated hologram (CGH) for better error calibration. We present a method that will measure large aspheres to a greater level of accuracy than is presently possible. We use segmented and superposed CGH elements to certify and calibrate null lens errors absolutely to a high degree of accuracy. In such holograms two different phase functions are encoded on the CGH by means of aperture division. One subaperture generates a spherical wavefront that is used to determine the pattern errors of the hologram while the second subaperture reconstructs an aspherical wavefront used to calibrate the wavefront errors of the null lens. This careful calibration process involves the removal of both axisymmetric and non-axisymmetric errors in the null test. Once this is accomplished, the null lens may be used to test the asphere to a high degree of accuracy. Our initial results show that we can test 4-meter class aspheric mirrors to better than 1nm rms surface error. In current experiments we have set a goal of measuring such mirrors to better than lnm rms surface error.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
Volume6721
DOIs
Publication statusPublished - 2007
Event3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies, AOMATT 2007: Large Mirrors and Telescopes - Chengdu, China
Duration: Jul 8 2007Jul 12 2007

Other

Other3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies, AOMATT 2007: Large Mirrors and Telescopes
CountryChina
CityChengdu
Period7/8/077/12/07

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Keywords

  • Aspheres
  • Computer-generated holograms
  • Interferometry
  • Large mirrors
  • Null-test

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Condensed Matter Physics

Cite this

Mallik, P. C. V., Zehnder, R., Burge, J. H., & Poleshchuk, A. (2007). Absolute calibration of null correctors using dual computer-generated holograms. In Proceedings of SPIE - The International Society for Optical Engineering (Vol. 6721). [672104] https://doi.org/10.1117/12.782680