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Proceedings Paper

High-accuracy piston error measurement with a large capture range based on coherent diffraction
Author(s): Weirui Zhao; Lu Zhang; Yuejin Zhao; Liquan Dong; Mei Hui
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Paper Abstract

Segmented and deployable primary mirror telescope is adopted to realize a higher resolution observation. Meanwhile the cophasing error is introduced. The piston error between the segments should be smaller than λ/20 RMS to achieve a diffraction-limited imaging. However the initial piston error is about 200 μm. A high-accurate piston error measurement with a large capture range is needed. We propose a method to simultaneously detect the multi-piston errors between segments with a high accuracy in a large capture range. A mask with a sparse sub-aperture configuration is set in the exit-pupil plane of the telescope to sample the wave from the segments. The relation between the piston error of any two segments and the amplitude of the modulation transfer function (MTF) sidelobes (MTFnph) is derived according to the Fourier optics principle. The piston error can be retrieved by this relation after measuring the MTFnph. Simulation and experiments have been carried out to validate the feasibility of the method. The results state that this method's capture range is the operating light’s coherence length, the accuracy is 0.026λ RMS (λ = 633 nm). The MTF model of a mask with sparse multi-subaperture configuration is established. The arrangement rules, to avoid the sidelobes overlapping, are obtained. The mask with a sparse 18 subaperture configuration is designed, which makes the MTF sidelobes distribution non-redundant. Consequently, just a mask with a sparse multi-subaperture configuration is needed, simultaneous detection of the multi-piston errors can be realized in term of this method.

Paper Details

Date Published: 21 June 2019
PDF: 11 pages
Proc. SPIE 11056, Optical Measurement Systems for Industrial Inspection XI, 110563B (21 June 2019); doi: 10.1117/12.2525311
Show Author Affiliations
Weirui Zhao, Beijing Institute of Technology (China)
Lu Zhang, Beijing Institute of Technology (China)
Yuejin Zhao, Beijing Institute of Technology (China)
Liquan Dong, Beijing Institute of Technology (China)
Mei Hui, Beijing Institute of Technology (China)

Published in SPIE Proceedings Vol. 11056:
Optical Measurement Systems for Industrial Inspection XI
Peter Lehmann; Wolfgang Osten; Armando Albertazzi Gonçalves Jr., Editor(s)

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