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Proceedings Paper

Freeform metrology using swept-source optical coherence tomography with custom pupil-relay precision scanning configuration
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Paper Abstract

The recent advances in the optics manufacturing industry to achieve the capability of fabricating rotationally nonsymmetric optical quality surfaces have considerably stimulated the optical designs with freeform components. This opens up new horizons for novel optical systems with larger fields of view and higher performance, or significantly more compact in volume at equal performance compared to conventional systems. A bottleneck to the broad industrial applications of freeform optics remains the lack of a high performance optical metrology tool capable of measuring significant surface departures and slopes of the parts. To address this issue, we have developed a fiber-based swept-source optical coherence tomography (SS-OCT) system for point-cloud freeform metrology, where two-axis galvanometer scanners are leveraged for high-speed lateral scans. We specifically designed a custom all-reflective achromatic pupil relay system to achieve a diffraction-limited scanning configuration. Coupled with a large field-of-view (FOV) telecentric scan lens, the imaging covers 28.9 mm × 28.9 mm FOV with 35 μm lateral resolution and more than 600 μm depth of focus. Freeform metrology is demonstrated for an Alvarez surface of 400 μm surface sag. The high sensitivity of the SS-OCT system allows for capturing the slope variations of the part up to the maximum slope that is 5 degrees in this case. Specific surface reconstruction, rendering and fitting algorithms were developed to evaluate the metrology results and investigate the accuracy and precision of the measurements.

Paper Details

Date Published: 11 October 2015
PDF: 5 pages
Proc. SPIE 9633, Optifab 2015, 96331A (11 October 2015); doi: 10.1117/12.2195939
Show Author Affiliations
Jianing Yao, The Institute of Optics, Univ. of Rochester (United States)
Di Xu, The Institute of Optics, Univ. of Rochester (United States)
Nan Zhao, The Institute of Optics, Univ. of Rochester (United States)
Changchun Institute of Optics, Fine Mechanics and Physics (China)
Univ. of Chinese Academy of Sciences (China)
Jannick P. Rolland, The Institute of Optics, Univ. of Rochester (United States)

Published in SPIE Proceedings Vol. 9633:
Optifab 2015
Julie L. Bentley; Sebastian Stoebenau, Editor(s)

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