16 October 2017 Thermal instability of BK7 and how it affects the manufacturing of large high precision surfaces
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Proceedings Volume 10448, Optifab 2017; 104481M (2017) https://doi.org/10.1117/12.2279807
Event: SPIE Optifab, 2017, Rochester, New York, United States
When manufacturing precision optical surfaces of relatively larger sizes it is critical to understand the thermal stability of the substrate material. The material properties associated with thermal homogenization are commonly reviewed and soak schedules are created. These schedules ensure a surface under test is in a stable state and is ready for wavefront measurement with an interferometer. However with some materials such as N-BK7, standard soak schedules may not be enough. This paper shows the thermal challenges associated with manufacturing precision optical surfaces when the substrate material is N-BK7, and how the issue can be easily confused with poor metrology. Throughout the manufacturing of precision optical surfaces, the substrates are exposed to varying heat sources and loads. During the manufacturing of lenses greater than 4 inches in diameter we have observed permanent deformation of the optical surface as a result of exposure to temperatures well below the glass strain point. While the reasons why the change occurs is not yet well understood, the result is well documented and was recently observed during the manufacturing of a 15 inch diameter spherical mirror. We use this lens as a case study highlighting the challenges associated with this phenomenon.
© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael Hyman, Michael Hyman, Matthew Brunelle, Matthew Brunelle, Nohl Schluntz, Nohl Schluntz, Michael Gregory, Michael Gregory, Mark Notargiacomo, Mark Notargiacomo, Greg Frisch, Greg Frisch, Jeremiah Triftshauser, Jeremiah Triftshauser, } "Thermal instability of BK7 and how it affects the manufacturing of large high precision surfaces", Proc. SPIE 10448, Optifab 2017, 104481M (16 October 2017); doi: 10.1117/12.2279807; https://doi.org/10.1117/12.2279807


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