Model-free optical surface reconstruction from deflectometry data

L. R. Graves, H. Choi, W. Zhao, C. J. Oh, P. Su, T. Su, D. W. Kim

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations


Deflectometry is a metrology method able to measure large surface slope ranges that can achieve surface reconstruction accuracy similar to interferometry, making it ideal for freeform metrology. While it is a non-null method, deflectometry previously required a precise model of the unit under test to accurately reconstruct the surface. However, there are times when no such model exists, such as during the grinding phase of an optic. We developed a model-free iterative data processing technique which provides improved deflectometry surface reconstruction of optics when the correct surface model is unknown. The new method iteratively reconstructs the optical surface, leading to a reduction in error in the final reconstructed surface. Software simulations measuring the theoretical performance limitations of the model-free processing technique as well as a real-world test characterizing actual performance were performed. The method was implemented in a deflectometry system and a highly freeform surface was measured and reconstructed using both the iterative technique and a traditional non-iterative technique. The results were compared to a commercial interferometric measurement of the optic. The reconstructed surface departure from interferometric results was reduced from 44.39 μm RMS with traditional non-iterative deflectometry down to 5.20 μm RMS with the model-free technique reported.

Original languageEnglish (US)
Title of host publicationOptical Manufacturing and Testing XII
EditorsRay Williamson, Dae Wook Kim, Rolf Rascher
ISBN (Electronic)9781510620551
StatePublished - 2018
EventOptical Manufacturing and Testing XII 2018 - San Diego, United States
Duration: Aug 20 2018Aug 22 2018

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherOptical Manufacturing and Testing XII 2018
Country/TerritoryUnited States
CitySan Diego


  • Deflectometry
  • Freeform
  • Metrology
  • Model-free

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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