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21 August 2020 Cascade optical coherence tomography (C-OCT) towards freeform metrology
Di Xu, Andres Garcia Coleto, Zhenkun Wen, Benjamin Moon, Jonathan C. Papa, Michael Pomerantz, John C. Lambropoulos, Jannick P. Rolland
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Proceedings Volume 11490, Interferometry XX; 114900K (2020) https://doi.org/10.1117/12.2567080
Event: SPIE Optical Engineering + Applications, 2020, Online Only
Abstract
Surface form metrology for freeform optical components is a significant challenge that impacts the entire process chain. One of the main aims is that the metrology technique provides sufficiently low measurement uncertainty within a reasonable measurement time. We developed a non-contact, non-part-specific cascade optical coherence tomography (COCT) technique within this metrology context. C-OCT utilizes a primary and a secondary interferometer in a cascade that transforms a difficult-to-measure optical path difference (OPD), which encodes the freeform sag in this case, into a more readily measured OPD in the secondary interferometer. To enable high-speed measurements, we developed the secondary interferometer based on a rotating optical cube. A custom telecentric objective lens and a custom pupil relay enable optical scanning over the sample surface. Experimental results validate the C-OCT technique with consecutive single-point measurements showing precision of ±26 nm (~λ/24 at the He-Ne wavelength) and a preliminary flat surface measurement demonstrating 22 nm RMS (~λ/28) over a central 20 mm diameter region. Developments on the system are underway towards surface measurements on freeform optical components.
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Di Xu, Andres Garcia Coleto, Zhenkun Wen, Benjamin Moon, Jonathan C. Papa, Michael Pomerantz, John C. Lambropoulos, and Jannick P. Rolland "Cascade optical coherence tomography (C-OCT) towards freeform metrology", Proc. SPIE 11490, Interferometry XX, 114900K (21 August 2020); https://doi.org/10.1117/12.2567080
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KEYWORDS
Interferometers
Mirrors
Optical coherence tomography
Metrology
Freeform optics
Objectives
Optical components
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