Cheng Jian, Wang Jinghe, Peng Enhong, Yang Hao, Chen Hao, Chen Mingjun, Tan Jiubin
Opt Express. 2020 Mar 16;28(6):8764-8782. doi: 10.1364/OE.388741.
Manufacturing-induced surface defects are deemed as a potential source, leading the laser-induced damage threshold (LIDT) of the actual KDP crystal optics to be much lower than the intrinsic one. However, the underlying mechanisms have not been fully recognized. We explore the combined modulation of incident laser light by multiple scratches and their effects on laser damage performance of KDP optics by modeling the light intensifications and performing a laser damage test. Under the combined modulation of multiple scratches, enhanced hot spots are generated due to the focusing effects of convex lens profiles surrounded by the neighboring scratches. The combined modulation actions are much stronger than that of a single scratch. The relative light intensities (Is) caused by multiple scratches can reach up to two times, and the number of hot spots (IPs) are four times as large as those by a single scratch. The Is exhibit a general, increasing tendency as the scratch density increases. But for the case of double total reflections of rear-surface scratches, the totally reflected lights are transmitted through neighboring scratches, resulting in decreasing tendency of Is. The tested LIDTs and optical transmittances of multiple scratches present a gradual, decreasing tendency with the increase of scratch density, which agrees with the simulation results. Besides, the simulated light intensifications could well explain the locations of laser damage, which further verify the role of multiple scratches in lowering the laser damage resistance.
制造过程中产生的表面缺陷被视为一个潜在来源，导致实际磷酸二氢钾（KDP）晶体光学元件的激光诱导损伤阈值（LIDT）远低于其本征值。然而，其潜在机制尚未得到充分认识。我们通过对光强进行建模并开展激光损伤测试，探究了多条划痕对入射激光的联合调制及其对KDP光学元件激光损伤性能的影响。在多条划痕的联合调制下，由于相邻划痕包围的凸透镜轮廓的聚焦效应，会产生增强的热点。联合调制作用比单个划痕的要强得多。多条划痕引起的相对光强（Is）可达单个划痕的两倍，热点数量（IPs）是单个划痕的四倍。随着划痕密度增加，Is总体呈上升趋势。但对于后表面划痕发生两次全反射的情况，全反射光透过相邻划痕，导致Is呈下降趋势。多条划痕的测试LIDT和光学透过率随划痕密度增加呈逐渐下降趋势，这与模拟结果相符。此外，模拟的光强增强能够很好地解释激光损伤的位置，这进一步验证了多条划痕在降低激光损伤抗性方面的作用。
