A nodule dome removal strategy to improve the laser-induced damage threshold of coatings

Various coatings in high-power laser facilities suffer from laser damage due to nodule defects. We propose a nodule dome removal (NDR) strategy to eliminate unwanted localized E-field enhancement caused by nodule defects, thereby improving the LIDT of laser coatings. It is theoretically demonstrated that the proposed NDR strategy can reduce the localized E-field enhancement of nodules in mirror coatings, polarizer coatings, and beam splitter coatings. A UV mirror coating is experimentally demonstrated using the NDR strategy. The LIDT is improved to about 1.9 and 2.2 times for the UV mirror coating without artificial nodules and the UV mirror coating with artificial nodule seeds with a diameter of 1000 nm, respectively. The NDR strategy, applicable to coatings prepared by different deposition methods, improves the LIDT of laser coating without affecting other properties such as spectrum, stress, and surface roughness, indicating its broad applicability in high-LIDT laser coatings.

高功率激光装置中的各类光学涂层常因结节缺陷引发激光损伤。本文提出一种结节穹顶去除（nodule dome removal, NDR）策略，用以消除结节缺陷导致的有害局部电场增强效应，进而提升激光涂层的激光诱导损伤阈值（Laser-Induced Damage Threshold，简称LIDT）。理论研究证实，所提NDR策略可降低反射镜涂层、偏振片涂层以及分光镜涂层中结节的局部电场增强。针对紫外反射镜涂层的实验验证结果显示：未含人工结节的紫外反射镜涂层，与植入直径1000纳米人工结节的紫外反射镜涂层，其LIDT分别提升至原有水平的约1.9倍和2.2倍。该NDR策略适用于不同沉积工艺制备的涂层，可在不影响光谱、应力及表面粗糙度等其他性能的前提下提升激光涂层的LIDT，表明其在高LIDT激光涂层领域具备广泛的应用前景。