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14 May 2007 Accurate interferometric measurements of mild aspheres without null correction
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Traditionally, the most accurate measurements of aspheric surfaces have relied on interferometric null tests. These usually require "null correction" optics, which often take significant time and expense to design and fabricate, and are specific to a particular asphere prescription. Alignment and calibration of the null correction optics can also be quite difficult. Thus there is a significant benefit to a flexible, accurate, "operator-friendly" alternative to the null test. Testing aspheres without null correction (using a spherical wavefront) has been very limited. A typical interferometer can acquire only a few micrometers of fourth-order aspheric departure before the interference fringes become too dense to resolve. Other "non-null" issues include accounting for the part's aspheric shape and optical aberrations of the interferometer. QED's SSI-ATM addresses these limitations, allowing a standard Subaperture Stitching Interferometer (SSI®) to automatically measure mild aspheric surfaces. The basic principles of how subaperture stitching enhances asphere capability are reviewed. Furthermore, SSI-A measurements from real aspheres are presented, along with null test measurements where available.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Paul E. Murphy, Jon Fleig, Stephen O'Donohue, and Gary DeVries "Accurate interferometric measurements of mild aspheres without null correction", Proc. SPIE 10316, Optifab 2007: Technical Digest, 103160O (14 May 2007);

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