Measuring large amplitude surface figure error using coordinate metrology

Manal Khreishi, Raymond G. Ohl, Ryan McClelland, Ron Shiri, Tilak Hewagama, Shahid Aslam, Melville P. Ulmer, Edgar Canavan, Rongguang Liang

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Advances in optical testing are as important as advances in fabrication because one can make only what one can measure. A high-precision metrology capability is utilized to close the gap between interferometric testing and lower precision metrology, laser radar, or contact-probe-based coordinate measuring machines (CMM) to accurately measure surfaces with large form error. This nearly universal optical testing method employs a precision CMM equipped with a non-contact, confocal probe. This technique was developed to characterize and align a broad spectrum of optical surfaces including ones with high slopes that are nearly impossible to measure using traditional interferometric testing without custom-made optics. Optical components covering a wide range of prescriptions, such as large convex conics, high-sloped aspherics, grazing-incidence x-ray optics, and highly deformed flats, were successfully measured. The resulting data were processed using custom-developed routines to determine the optic's alignment, the departure from design surface, and the as-built prescription parameters. This information was used to verify and guide the development and fabrication of novel optics.

Original languageEnglish (US)
Article number084103
JournalOptical Engineering
Issue number8
StatePublished - Aug 1 2021


  • adaptive optics
  • confocal probe
  • coordinate measuring machine
  • large convex mirror
  • optical coordinate metrology
  • optical shop testing
  • surface deformation
  • universal optical testing
  • x-ray optics

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • General Engineering


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