J. Eur. Opt. Soc.-Rapid Publ.
Volume 15, Number 1, 2019
|Number of page(s)||7|
|Published online||04 September 2019|
Improving the calibration of phase measuring deflectometry by a polynomial representation of the display shape
BIAS-Bremer Institut für angewandte Strahltechnik, Klagenfurter Str.5, 28359, Bremen, Germany
2 University of Bremen, Faculty of Physics and Electrical Engineering, Otto-Hahn-Allee 1 and MAPEX Center for Materials and Processes, 28359, Bremen, Germany
Accepted: 15 August 2019
Background: Phase measuring deflectometry is a highly precise and full field metrology technique for specular surfaces based on the distortion of known reference patterns observed as a reflection at the surface under test. Typically, liquid crystal displays are employed to provide the required patterns. Due to a lack of research, these displays are used without sufficient calibration.
Methods: In this work, we present an enhanced calibration for phase measuring deflectometry, taking flatness deviations of the display surface into account. The display shape is modelled as a polynomial surface whose coefficients are determined by minimizing the retrace error in a global optimization procedure during calibration. This approach does not require any additional measurements or hardware. Improvements due to the enhanced calibration model are qualified experimentally using a flat and a spherical concave mirror.
Results and conclusion: The model-based parameterization of the display surface yields significant improvement on both samples. The peak to valley (PV) of measured deviations on the plane mirror are reduced by 67% to 0.55 μm. Measuring the spherical sample without the display parameterization leads to a rather large shape deviation of 33.40 μm PV which is reduced by 94% to 1.98 μm. The viability of our approach confirms the dominant role of flatness deviations of the display surface as an error source in absolute shape measurement using phase measuring deflectometry.
Key words: Deflectometry / Absolute surface metrology / Displays
© The Author(s) 2019
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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