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Proceedings Paper

Precision glass molding of freeform optics
Author(s): Dustin Gurganus; Joseph D. Owen; Brian S. Dutterer; Spencer Novak; Alan Symmons; Matthew A. Davies
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Paper Abstract

Precision glass molding is a viable process for the cost-effective volume production of freeform optics. Process development is complex, requiring iterative trials of mold manufacture and metrology, glass mold prototyping, metrology and functional testing. This paper describes the first iteration in the development of a process for an Alvarez lens for visible light. The challenges of this optic are extremely tight band-RMS tolerances on a freeform shape over a maximum clear aperture of 45 mm, a 16:1 aspect ratio and a freeform departure of 329 micrometers. A freeform glass mold for an Alvarez lens was manufactured by coordinated-axis diamond turning in a mold substrate using a custom tool error correction method. The results of prototype precision glass molding are also reported. Mold surfaces and molded optical surfaces are analyzed with scanning white light interferometry. A surface roughness of approximately 3 nm RMS is obtained for both the mold substrate and the glass optic with high-fidelity reproduction of micro-surface structure in the glass. These measurements also identify challenging areas, particularly the presence of mid-spatial frequency errors on the optic originating from the machine thermal control system. The form of the molds was also measured with a profilometer; however, the mold surface does not agree with the expected prescription with an overall deviation in form of approximately 10 μm. The machining process is expected to have sub-micrometer error and the sources of this discrepancy are still being determined. Metrology of the glass optics is currently in progress.

Paper Details

Date Published: 14 September 2018
PDF: 11 pages
Proc. SPIE 10742, Optical Manufacturing and Testing XII, 107420Q (14 September 2018); doi: 10.1117/12.2320574
Show Author Affiliations
Dustin Gurganus, The Univ. of North Carolina at Charlotte (United States)
Joseph D. Owen, The Univ. of North Carolina at Charlotte (United States)
Brian S. Dutterer, The Univ. of North Carolina at Charlotte (United States)
Spencer Novak, LightPath Technologies, Inc. (United States)
Alan Symmons, LightPath Technologies, Inc. (United States)
Matthew A. Davies, The Univ. of North Carolina at Charlotte (United States)

Published in SPIE Proceedings Vol. 10742:
Optical Manufacturing and Testing XII
Ray Williamson; Dae Wook Kim; Rolf Rascher, Editor(s)

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