Visualization of nanometer scale defects responsible for optical loss and laser induced breakdown in binary coating materials for the UV spectral region

如今，紫外光光学被认为是光子学和激光技术中许多创新应用的重要关键部件。在众多领域中，紫外激光材料加工、激光医学、特别是半导体光刻等领域对光学紫外光组件的质量提出了苛刻的挑战。组件的光学损耗和激光功率处理能力对激光概念及其应用的成功至关重要。根据基于光致电离损伤的理论预测，光学元件的激光击穿发生在低得多的辐照强度。几十年来，人们普遍认为光学损伤阈值的降低和光学损耗的增加都是由纳米颗粒、空洞、界面缺陷以及化学计量缺陷等缺陷引起的。尽管这一理论在光学界得到了广泛的认可，但大多数这些建议的缺陷要么是直接不可见的，要么是不可能直接验证它们对损伤行为的影响。在拟议的研究中，计划识别和研究紫外激光应用光学涂层中光学损失和激光击穿的主要贡献。正如前面提到的，这一挑战的原因是建议的缺陷尺寸为几纳米。该建议中用于识别导致光学击穿的纳米缺陷的方法是双轨的：一方面，应在现有光学涂层中加入相应的人工缺陷以再现光学损伤行为，另一方面应开发光学探头技术，以获得纳米尺度上的光学性质的形貌。

Nowadays UV optics are considered as important key components for many innovative applications in photonics andlaser technology. Among many others, the large areas of UV laser material processing, laser medicine or particularly,semiconductor lithography impose demanding challenges onto the quality of optical UV-components. Both the opticalloss and the laser power handling capability of the components are of outmost importance for the success of a laserconcept and its applications. Laser induced breakdown of optical components occurs at much lower irradiationintensity as predicted by theories based on damage due to photoionization. Since decades, it is a well-acceptedinterpretation that the reduction of optical damage threshold, and also the increase of optical losses are caused bydefects, such as nanometer-sized particles, voids, and the interfaces as well as stoichiometric deficiencies. Thesedefects could be embedded in the thin coating layer, at layer- or substrate interfaces, or below the substrate surface.Despite the broad acceptance of this theory in the optical community, mostly these suggested defects either remainedinvisible for direct observation, or it was not possible to verify their influence on the damage behavior directly.In the proposed research endeavor, it is planned to identify and study the dominant contributions to optical losses andlaser induced breakdown in optical coatings for UV-laser applications. As mentioned before, the reason for thischallenge is the suggested defect size of a few nanometers. The approach within this proposal for identifying nanodefectsresponsible for optical breakdown, is double-tracked: On the one hand, corresponding artificial defects shall beincorporated in state of the art optical coatings to reproduce optical damage behavior, and on the other hand an opticalprobe techniques shall be developed, to obtain topographies of optical properties on the nanometer scale.