Measurement of mild aspheric surfaces with subaperture stitching interferometry

Paul E. Murphy; Greg Forbes; Jon Fleig

doi:10.1117/12.605743

2 May 2005 Measurement of mild aspheric surfaces with subaperture stitching interferometry; Technical Digest

Paul E. Murphy, Greg Forbes, Jon Fleig

Proceedings Volume 10315, Optifab 2005: Technical Digest; 103150L (2005) https://doi.org/10.1117/12.605743
Event: Optifab 2005, 2005, Rochester, NY, United States

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.

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Paul E. Murphy, Greg Forbes, and Jon Fleig "Measurement of mild aspheric surfaces with subaperture stitching interferometry; Technical Digest", Proc. SPIE 10315, Optifab 2005: Technical Digest, 103150L (2 May 2005); https://doi.org/10.1117/12.605743

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KEYWORDS

Aspheric lenses

Interferometers

Stitching interferometry

Phase measurement

Spherical lenses

Cameras

Microscopes

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