NSF/DFG Collaboration Brinksmeier/Riemer/Lucca: "Ultra-Precision Machining and Near Surface Damage Evolution in Single Crystal Fluorides for Advanced Optics"

• Applicant: Dr.-Ing. Oltmann Riemer
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387318746

NSF/DFG Collaboration Brinksmeier/Riemer (Universität Bremen), Lucca (Oklahoma State University); NSF proposal number # 1727244:The research objective of this proposed study is to test the hypothesis that the degradation in optical performance of single crystal calcium fluoride (CaF2), which has been finished by ul-tra-precision machining, is directly related to the nature and extent of the near surface dam-age introduced. Ultra-precision machining experiments based on linear planing with round nose single crystal diamond tools will be used to determine the critical depth of cut to produce a non-fractured surface for a given crystal orientation.Based on these findings, linear planing and face turning experiments will be performed to generate surfaces for which the surface and subsurface state can be evaluated. Channeling Rutherford backscattering spectrometry (channeling RBS), cross-sectional transmission elec-tron microscopy (XTEM) and high resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD) will be used to provide a quantitative characterization of the sub-surface. The optical performance of the surface will then be assessed by measuring trans-missivity using Ultraviolet-Visible (UV-Vis) spectroscopy and birefringence using a polarime-ter. The project is an international collaboration between Oklahoma State University (OSU), the Laboratory for Precision Machining (LFM) at the University of Bremen, Los Alamos Na-tional Laboratory (LANL) and Carl Zeiss Jena GmbH.The mechanisms responsible for the degradation in optical quality caused by the ultra-precision machining of single crystal fluorides, in particular calcium fluoride (CaF2) are not scientifically understood. This lack of understanding is limiting applications where diamond turning, as opposed to polishing, is required, e.g., nanometer precision aspheric or free-form optics. It is expected that this study will contribute to new fundamental understanding of both the nature and extent of subsurface damage introduced into these brittle, optical materials by ultra-precision (single point diamond) machining. It is envisioned that the findings of this work will be applicable to a range of single crystal alkaline earth fluorides which are finding emerg-ing uses in optical applications. The study will establish a quantitative link between spectrally resolved optical performance and subsurface damage. It will determine whether the degrada-tion in optical performance of single crystal calcium fluoride is directly related to the nature and extent of the near surface damage introduced.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Professor Dr.-Ing. Ekkard Brinksmeier
• Cooperation Partner: Professor Dr. Don A. Lucca