Calibration methods for a dual-wavelength interferometer system

Yanqi Zhang, Martin Tangari Larrategui, Thomas G. Brown, Jonathan D. Ellis

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

2 Scopus citations


Multiple wavelength interferometry has long been considered an option for the measurement of large aspheric slope departures. In particular, a synthetic wavelength offers a variety of approaches by which large phase excursions can be unwrapped. Using multiple wavelengths can create collimation and magnification mismatch errors between the individual wavelengths that arise during beam expansion and propagation. Here, we present and analyze alignment and calibration methods for a dual-wavelength interferometer that can significantly reduce both misalignment errors and chromatic aberrations in the system. To correct for misalignment, a general method is described for the alignment of a dual-wavelength interferometer, including the alignment of lasers, beam expanders, beam splitters for combining beams and for compensating errors in the reference surface, and the fringe imaging system. A Fourier transform test at the detector surface was conducted to validate that there is essentially no magnification difference between two wavelengths resulting from misalignment of optical system. For the chromatic aberration introduced by the optical elements in the system, a ray-trace model of the interferometer has been established, to simulate the chromatic effect that optical elements will have on the measurement results. As an experimental test, we examine an off-axis spherical mirror in a non-null condition using a highly aliased interferogram. The above alignment methods and the results are analyzed based on the simulated system errors. Using this method, we demonstrate a measured surface profile of deviation of 1/25 which is comparable to a direct measurement profile of the surface on axis using a Fizeau interferometer.

Original languageEnglish (US)
Title of host publicationOptical System Alignment, Tolerancing, and Verification XII
EditorsJose Sasian, Richard N. Youngworth
ISBN (Electronic)9781510620650
StatePublished - 2018
EventOptical System Alignment, Tolerancing, and Verification XII 2018 - San Diego, United States
Duration: Aug 19 2018Aug 20 2018

Publication series

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


OtherOptical System Alignment, Tolerancing, and Verification XII 2018
Country/TerritoryUnited States
CitySan Diego


  • Dual-wavelength interferometry
  • Surface metrology

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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