Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification

Liu, Qi; Cheng, Jian; Liao, Zhirong; Yang, Hao; Zhao, Linjie; Chen, Mingjun

Abstract

© 2019 Elsevier Ltd Micro-milling has been accepted as the most promising method to repair the micro-defects on the surface of KH2PO4 (KDP) optics. However, surface tool marks are inevitably introduced during the micro-milling repairing process, and could possess great potential risks in lowering the laser-induced damage threshold of KDP optics. The primary cause of laser damage growth of nonlinear crystals has been considered as its internal light intensification. In this work, how the tool marks impact the incident laser modulation as well as the laser-induced damage resistance of micro-milled KDP optics was theoretically and experimentally investigated. The results indicate that periodic tool marks can cause diffraction effect and result in significant relative light intensity modulation (IRmax), up to 5.6 times higher than that inside smooth crystal surfaces. Although the change trends of IRmax with respect to tool marks on both surfaces of KDP optics are similar, the IRmax induced by the rear-surface tool marks is nearly twice higher than that induced by the front-surface tool marks, which means the rear surface with tool marks are more vulnerable to be damaged. The period of tool marks determines the modulation degree and distribution patterns of light intensity inside KDP crystal while the residual height of tool marks can only slightly regulate the modulation degree of light intensity. The tool marks with a period of 1 μm normally give rise to serious light intensification and should be strictly excluded, while the period of tool marks from 10 μm to 20 μm is conducive to the laser damage resistance of micro-milled KDP optics, which were verified by the tests of transmittance capacity and laser damage resistance, and is supposed to be preferred in the actual repairing process of full-aperture KDP optics.

Citation

Liu, Q., Cheng, J., Liao, Z., Yang, H., Zhao, L., & Chen, M. (2019). Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification. Optics and Laser Technology, 119, Article 105610. https://doi.org/10.1016/j.optlastec.2019.105610

• Journal Article Type: Article
• Acceptance Date: May 27, 2019
• Online Publication Date: Jun 12, 2019
• Publication Date: Nov 1, 2019
• Deposit Date: Sep 9, 2019
• Publicly Available Date: Jun 13, 2020
• Journal: Optics and Laser Technology
• Print ISSN: 0030-3992
• Electronic ISSN: 1879-2545
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 119
• Article Number: 105610
• DOI: https://doi.org/10.1016/j.optlastec.2019.105610
• Keywords: KDP crystal; Laser damage; Light intensity modulation; Micro ball-end milling; Tool marks; Surface topography
• Public URL: https://nottingham-repository.worktribe.com/output/2592241
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0030399219303305?via%3Dihub
• Additional Information: This article is maintained by: Elsevier; Article Title: Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification; Journal Title: Optics & Laser Technology; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.optlastec.2019.105610; Content Type: article; Copyright: © 2019 Elsevier Ltd. All rights reserved.
• Contract Date: Sep 11, 2019