Measurement of high-departure aspheric surfaces using subaperture stitching with variable null optics

Paul Murphy*, Gary Devries, Jon Fleig, Gregory Forbes, Andrew Kulawiec, Dragisha Miladinovic

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

24 Citations (Scopus)


Aspheric surfaces can provide significant benefits to optical systems, but manufacturing high-precision aspheric surfaces is often limited by the availability of surface metrology. Traditionally, aspheric measurements have required dedicated null correction optics, but the cost, lead time, inflexibility, and calibration difficulty of null optics make aspheres less attractive. In the past three years, we have developed the Subaperture Stitching Interferometer for Aspheres (SSI-A®) to help address this limitation, providing flexible aspheric measurement capability up to 200 waves of aspheric departure from best-fit sphere. Some aspheres, however, have hundreds or even thousands of waves of departure. We have recently developed Variable Optical Null (VONTM) technology that can null much of the aspheric departure in a subaperture. The VON is automatically reconfigurable and is adjusted to nearly null each specific subaperture of an asphere. The VON provides a significant boost in aspheric measurement capability, enabling aspheres with up to 1000 waves of departure to be measured, without the use of null optics that are dedicated to each asphere prescription. We outline the basic principles of subaperture stitching and the Variable Optical Null, demonstrate the extended capability provided by the VON, and present measurement results from our new Aspheric Stitching Interferometer (ASITM).

Original languageEnglish
Title of host publicationOptical Manufacturing and Testing VIII
Subtitle of host publicationProceedings of SPIE
EditorsJames H. Burge, Oliver W. Fähnle, Ray Williamson
Place of PublicationBellingham, WA
Number of pages9
ISBN (Print)9780819477163
Publication statusPublished - 2009
Externally publishedYes
EventOptical Manufacturing and Testing VIII - San Diego, CA, United States
Duration: 4 Aug 20095 Aug 2009


OtherOptical Manufacturing and Testing VIII
Country/TerritoryUnited States
CitySan Diego, CA


  • ASI
  • Asphere
  • Interferometry
  • Metrology
  • SSI®
  • Subaperture stitching
  • Variable optical null
  • VON


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