Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification
Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification
复制标题
微铣削KDP晶体表面刀痕的入射激光调制：数值模拟和实验验证
DOI：
10.1016/j.optlastec.2019.105610
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发表时间：
2019-11-01
影响因子：
5
通讯作者：
Chen, Mingjun
中科院分区：
文献类型：
--
作者：
Liu, Qi;Cheng, Jian;Chen, Mingjun
微铣削被认为是修复k2po4 （KDP）光学元件表面微缺陷最有前途的方法。然而，在微铣削修复过程中不可避免地会引入表面刀具痕迹，这对降低激光损伤阈值具有很大的潜在风险。非线性晶体激光损伤生长的主要原因是其内部光增强。本文从理论上和实验上研究了刀具标记对入射激光调制以及微铣削KDP光学器件抗激光损伤性能的影响。结果表明，周期性工具标记会引起衍射效应，导致明显的相对光强调制（I-Rmax），比光滑晶体表面高5.6倍。虽然两种KDP光学元件表面刀具刻痕的I-Rmax变化趋势相似，但后表面刀具刻痕引起的I-Rmax几乎是前表面刀具刻痕引起的I-Rmax的两倍，这意味着有刀具刻痕的后表面更容易被损坏。刀具刻痕的周期决定了KDP晶体内部光强的调制程度和分布规律，而刀具刻痕的残留高度只能轻微调节光强的调制程度。周期为1 μ m的刀具标记通常会引起严重的光强，应严格排除，而周期为10 μ m至20 μ m的刀具标记有利于微铣削KDP光学元件的抗激光损伤能力，通过透光能力和抗激光损伤测试验证了这一点，在全孔径KDP光学元件的实际修复过程中应优先考虑。
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 (I-Rmax), up to 5.6 times higher than that inside smooth crystal surfaces. Although the change trends of I-Rmax with respect to tool marks on both surfaces of KDP optics are similar, the I-Rmax 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 mu m normally give rise to serious light intensification and should be strictly excluded, while the period of tool marks from 10 mu m to 20 mu m 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.