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Proceedings Paper

Measurement of mild aspheric surfaces with subaperture stitching interferometry
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Paper Abstract

Subaperture stitching is a well-known technique for extending the effective aperture range of phase measuring interferometers. In the past, stitching has successfully been applied to improve the lateral coverage and/or resolution of plano interferometers (including interference microscopes). More recently, QED Technologies has developed a subaperture stitching interferometer (SSI®) for automatic stitching of spherical surfaces, including hemispheres. But stitching can also extend the amount of aspheric departure that can be measured in a non-null test. Conventional interferometers have some capability to measure mild aspheric surfaces without null correction. The interference fringe resolution of the camera limits the asphericity that can be measured, while the difficulty in inferring the surface form from the measured phase degrades accuracy. Therefore, commercially available interferometers can only measure a few micrometers of fourth-order aspheric departure. Furthermore, standard measurement software does not compensate for the aspheric shape or for the interferometer imaging errors present in a non-null measurement. As a result, non-null aspheric measurements are more difficult, and less accurate, than a spherical null test. Examples are presented in this paper that illustrate these issues. Subaperture stitching can extend the testable aspheric departure of a non-null test. This has been demonstrated in the past on annular zones of near-null data. We present a more generally applicable and robust method of stitching non-null phase data, which can provide better accuracy and increased testable aspheric departure over an unstitched test.

Paper Details

Date Published: 2 May 2005
PDF: 3 pages
Proc. SPIE 10315, Optifab 2005: Technical Digest, 103150L (2 May 2005); doi: 10.1117/12.605743
Show Author Affiliations
Paul E. Murphy, QED Technologies (United States)
Greg Forbes, QED Technologies (United States)
Jon Fleig, QED Technologies (United States)

Published in SPIE Proceedings Vol. 10315:
Optifab 2005: Technical Digest
Robert E. Fischer; Masahide Katsuki; Matthias Pfaff; Kathleen A. Richardson, Editor(s)

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