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Proceedings Paper

Full-field deflectometry for detection of mid-spatial frequency errors of high-precision mirrors (Conference Presentation)
Author(s): Philippe Antoine; Luc Boussemaere; Arno Bouwens; Vincent Moreau; Benoit Borguet; Ksenia Sharshavina

Paper Abstract

Full-field deflectometry, which combines high-precision and robustness to external perturbations, is well adapted for the characterization of high-precision freeform mirrors. Instead of measuring the surface height map like interferometry does, the instrument will estimate the surface slopes in two perpendicular directions. The principle of the method is to measure the angular distribution by applying spatial filtering in the Fourier plane of the mirror under test. This method has been called phase-shifting Schlieren deflectometry Inspection of mirrors in terms of slopes instead surface height offers multiple advantages. In particular, deflectometry is well adapted for the detection of waviness, which is a mid-spatial frequency topography error. Waviness detection during the diamond turning process is critical since it is hard to remove afterwards by polishing. Keeping the mirror mounted in the lathe during the measurement of its shape will simplify the process since it will avoid misalignment when re-mounting the mirror in the lathe. The presentation will discuss the principles of phase-shifting Schlieren deflectometry, the performance specification based on the tolerance study of the four-mirror spectrometer, the design of the new instrument under development and finally preliminary measurements of freeform mirrors performed at AMOS with the mirror mounted in the lathe that demonstrate the capability of the instrument for the detection of mid-spatial frequency errors.

Paper Details

Date Published: 18 November 2019
Proc. SPIE 11175, Optifab 2019, 111751F (18 November 2019); doi: 10.1117/12.2536804
Show Author Affiliations
Philippe Antoine, LAMBDA-X sa (Belgium)
Luc Boussemaere, LAMBDA-X sa (Belgium)
Arno Bouwens, LAMBDA-X sa (Belgium)
Vincent Moreau, AMOS Ltd. (Belgium)
Benoit Borguet, AMOS Ltd. (Belgium)
Ksenia Sharshavina, AMOS Ltd. (Belgium)

Published in SPIE Proceedings Vol. 11175:
Optifab 2019
Blair L. Unger; Jessica DeGroote Nelson, Editor(s)

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