Absolute surface metrology by differencing spatially shifted maps from a phase-shifting interferometer

Optics Letters
E E Bloemhof

Abstract

Surface measurements of precision optics are commonly made with commercially available phase-shifting Fizeau interferometers that provide data relative to flat or spherical reference surfaces whose unknown errors are comparable to those of the surface being tested. A number of ingenious techniques provide surface measurements that are "absolute," rather than relative to any reference surface. Generally, these techniques require numerous measurements and the introduction of additional surfaces, but still yield absolute information only along certain lines over the surface of interest. A very simple alternative is presented here, in which no additional optics are required beyond the surface under test and the transmission flat (or sphere) defining the interferometric reference surface. The optic under test is measured in three positions, two of which have small lateral shifts along orthogonal directions, nominally comparable to the transverse spatial resolution of the interferometer. The phase structure in the reference surface then cancels out when these measurements are subtracted in pairs, providing a grid of absolute surface height differences between neighboring resolution elements of the surface under test. The full absolut...Continue Reading

References

Aug 24, 2006·Applied Optics·Ulf Griesmann
Sep 1, 1993·Applied Optics·C Ai, J C Wyant

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Citations

Jun 3, 2011·Optics Letters·Jun MaWolfgang Osten
Oct 3, 2013·Applied Optics·Weihong SongYongjian Wan
Mar 6, 2019·The Review of Scientific Instruments·F PolackD Dennetiere
Jul 21, 2015·Applied Optics·Weibo WangJiubin Tan
Jun 2, 2020·Optics Letters·Peyman Soltani, Ahmad Darudi

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