An automated subaperture stitching interferometer workstation for spherical and aspherical surfaces

Jon Fleig*, Paul Dumas, Paul E. Murphy, Greg W. Forbes

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

147 Citations (Scopus)


Subaperture stitching is a well-known technique for extending the effective aperture and dynamic range of phase measuring interferometers. Several commercially available instruments can automatically stitch flat surfaces, but practical solutions for stitching spherical and aspherical surfaces are inherently more complex. We have developed an interferometer workstation that can perform high-accuracy automated subaperture stitching of spheres, flats, and mild aspheres up to 200 mm in diameter. The workstation combines a six-axis precision stage system, a commercial Fizeau interferometer of 4″ or 6″ aperture, and a specially developed software package that automates measurement design, subaperture data acquisition, and the mathematical reconstruction of a full-aperture phase map. The stitching algorithm incorporates a general constrained optimization framework for compensating for several types of errors introduced by the interferometer optics and stage mechanics. These include positioning errors, viewing system distortion, and the system reference wave. We present repeatability data, and compare stitched full-aperture measurements made with two different transmission spheres to a calibrated full-aperture measurement. We also demonstrate stitching's ability to test larger aspheric departures on a 10 μm departure parabola, and compare the preliminary results with a full-aperture null test.

Original languageEnglish
Pages (from-to)296-307
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
Publication statusPublished - 2003
Externally publishedYes


  • Absolute calibration
  • Error compensation
  • Interferometry
  • Subaperture stitching


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