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Proceedings Paper

Definitions of criteria for assessing feasibility and measurability of freeform surfaces
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Paper Abstract

Regarding the progress of optical design in favor of freeform surfaces, it becomes necessary to scale their feasibility with appropriate criteria in order to get a standard between an optical designer and an optical manufacturer. Two criteria are necessary, one linked to polishing process and one appropriate for measurement limitation. First criterion can be the extension to freeform surfaces (defined here by first Zernike terms) of a previous criterion which was calculated using conical equation. This criterion is representative of surface’s curvatures fluctuations which limit polishing efficiency and can generate high frequency defects. The second criterion should take into account the difficulty to measure the surface as feasibility needs also good knowledge of the correction polishing cycle to be performed. Different solutions exist for an accurate measurement in the range of nm. As demonstrated in the article, slopes versus reference surface is the limiting factor for a majority of measurement solutions. Therefore the criterion will be linked to a slope parameter. The governing principle of these criteria is to remain close to some relevant physical dimensions. In this idea, the polishing feasibility criterion defined in this paper will be comparable to tool diameter of Computer Controlled Polishing which refers to equipment resolution of optical manufacturers. In the same idea, we project to define a dimensioned criterion for measuring feasibility which can be compared to engraving resolution for a given Computer Generated Hologram.

Paper Details

Date Published: 15 November 2019
PDF: 13 pages
Proc. SPIE 11175, Optifab 2019, 1117510 (15 November 2019); doi: 10.1117/12.2536663
Show Author Affiliations
Christian du Jeu, Thales SESO S.A.S. (France)
Julien Fourez, Thales SESO S.A.S. (France)
Hassan El Handrioui, Thales SESO S.A.S. (France)
Matthieu Gilles, Thales SESO S.A.S. (France)

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

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