title: Role of tool marks inside spherical mitigation pit fabricated by micro-milling on repairing quality of damaged KH2PO4 crystal.
abstract: Repairing initial slight damage site into stable structures by engineering techniques is the leading strategy to mitigate the damage growth on large-size components used in laser-driven fusion facilities. For KH2PO4 crystals, serving as frequency converter and optoelectronic switch-Pockels cell, micro-milling has been proven the most promising method to fabricate these stable structures. However, tool marks inside repairing pit would be unavoidably introduced due to the wearing of milling cutter in actual repairing process. Here we quantitatively investigate the effect of tool marks on repairing quality of damaged crystal components by simulating its induced light intensification and testing the laser-induced damage threshold. We found that due to the formation of focusing hot spots and interference ripples, the light intensity is strongly enhanced with the presence of tool marks, especially for those on rear surfaces. Besides, the negative effect of tool marks is mark density dependent and multiple tool marks would aggravate the light intensification. Laser damage tests verified the role of tool marks as weak points, reducing the repairing quality. This work offers new criterion to comprehensively evaluate the quality of repaired optical surfaces to alleviate the bottleneck issue of low laser damage threshold for optical components in laser-driven fusion facilities.
authors.affiliation: Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Ming-Jun
authors.initials: MJ
authors.lastname: Chen
authors.affiliation: Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Cheng
authors.affiliation: Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China.
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Yuan
authors.affiliation: Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liao
authors.affiliation: Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China.
authors.forename: Hai-Jun
authors.initials: HJ
authors.lastname: Wang
authors.affiliation: Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Jing-He
authors.initials: JH
authors.lastname: Wang
authors.affiliation: Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Ming-Quan
authors.initials: MQ
authors.lastname: Li