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Proceedings Paper

Absolute calibration of null correctors using dual computer-generated holograms
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Paper 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 1nm rms surface error.

Paper Details

Date Published: 21 November 2007
PDF: 16 pages
Proc. SPIE 6721, 3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes, 672104 (21 November 2007); doi: 10.1117/12.782680
Show Author Affiliations
Proteep C. V. Mallik, College of Optical Sciences, Univ. of Arizona (United States)
Rene Zehnder, College of Optical Sciences, Univ. of Arizona (United States)
James H. Burge, College of Optical Sciences, Univ. of Arizona (United States)
Alexander Poleshchuk, Institute of Automation and Electrometry (Russia)


Published in SPIE Proceedings Vol. 6721:
3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes

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