Optimizing "Dwell Time" for Higher Quality Optical Lenses
December 11, 2024

The work was featured on the cover of the journal. Credit: Advanced Manufacturing 5, 21 (2024).
The Science
Researchers propose a way to optimize "dwell time" in the computer-controlled fabrication of high-end optical surfaces.
The Impact
Determining optical dwell time – the brief hover time needed by automated tools that polish lenses, for example – enables higher quality, more specialized optics.
Summary
The rapid development of precision machining technologies over the last 10 years has resulted in great advances in high-end optical components. Some examples are the mirrors used in telescopes and extreme ultraviolet lithography (a process used to make integrated circuits) and the optics needed to focus and manipulate X-rays at synchrotron radiation and free-electron laser facilities. These optics demand the highest precision in surface shape, smoothness, and curvature.
This need for precision has rendered conventional polishing methods inadequate, and a variety of computer-controlled optical surfacing (CCOS) technologies have largely taken their place. The polishing tools used in CCOS are small to remove the smallest possible errors on the surface. As the tool is methodically swept across an optical surface, the “dwell time” that it spends at each point on the surface becomes a factor in the overall success of the CCOS method.
In this paper, we present a thorough review and analysis of eight well-known dwell time optimization methods. We classify these methods as either “function-form” or “matrix-form,” which are defined by the used mathematical approach. It is the first time that the connections and shared principles between these methods have been published in a journal.
The paper also proposes, for each method, an optimized implementation strategy which could expand their applicability. We back up these strategies with performance simulations, evaluating four critical criteria: accuracy, feasibility, efficiency, and flexibility. The authors conclude that a combination of two of the function-form methods — known as robust iterative Fourier transform-based dwell time optimization algorithm (RIFTA) and robust iterative surface extension (RISE) — and a matrix-form method, known as universal dwell time optimization (UDO), achieved the best balance across the four criteria.
With these methods, we have successfully developed the capability to fabricate synchrotron hard X-ray mirrors at sub-nanometer level precision. Moreover, our methods are now being implemented to support the fabrication of the Giant Magellan Telescope (GMT). Despite the successes, significant challenges remain to achieve similar precision for more aggressive surface shapes. To address these challenges, we are actively pursuing additional funding opportunities from the DOE’s Early Career Research Program and Field Work Proposals (FWPs).
The research was conducted at the Optical Metrology Laboratory at National Synchrotron Light Source II (NSLS-II). NSLS-II is a U.S. Department of Energy (DOE) Office of Science user facility located at DOE’s Brookhaven National Laboratory.
Download the research summary slide (PDF)
Contact
Tianyi Wang
Brookhaven National Laboratory
tianyi@bnl.gov
Xiaolong Ke
Xiamen University of Technology
kexiaolong@xmut.edu.cn
Publications
Tianyi Wang, Xiaolong Ke, Lei Huang, Qingqing Cui, Zili Zhang, Chunjin Wang, Hyukmo Kang, Weslin Pullen, Heejoo Choi, Daewook Kim, Vipender Negi, Qian Kemao, Yi Zhu, Stefano Giorgio, Philip Boccabella, Nathalie Bouet, Corey Austin, Mourad Idir. "A comprehensive review of dwell time optimization methods in computer-controlled optical surfacing." Light: Advanced Manufacturing 5, Article number: 21 (2024). DOI: https://doi.org/10.37188/lam.2024.021
Funding
This work was supported by the Accelerator and Detector Research Program, part of the Scientific User Facility Division of the Basic Energy Science Office of the U.S. Department of Energy (DOE), under the Field Work Proposal No. FWP-PS032. This research was performed at the Optical Metrology Laboratory at the National Synchrotron Light Source II, a U.S. DOE Office of Science User Facility operated by Brookhaven National Laboratory (BNL) under Contract No. DE-SC0012704. This work was performed under the BNL LDRD 17-016 “Diffraction limited and wavefront preserving reflective optics development.” This work was also supported by the Natural Science Foundation of Fujian Province, China, under grant number 2022J011245.
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