基于激光冲击波的光学薄膜后处理过程及机理研究

High power laser coatings are facing a series of more serious challenges including running on higher laser induced damage threshold (LIDT), higher repetitive frequency and higher stability. It not only involves the LIDT and damage growth under single- and multi-pulse irradiation respectively, but also the laser damage affected by optical performance and surface accuracy stability of coatings. In this project, we intend to use the laser shock wave technique as a post-processing method for coatings prepared by electron beam evaporation. By taking advantage of shock wave which can avoid thermal effect and act as mechanical behavior to improve the coating’s defect characteristic, microstructure and macro-mechanical property, is expected to ensure that coating could run on higher laser fluence with long term stability. The main research aspects will include: investigations on characterization and mechanism of LIDT improvement under single-pulse irradiation, as well as the long term running stability after post-processing of laser shock wave. Based on experiments and theoretical analysis, optimized technical parameters will be verified and the dynamic coupling process will be developed finally. This project will hopefully break the limitations of the existing technology, and provide a potential option for promoting coating to the direction of a much higher degree of laser resistance, accuracy and stability development.

大口径高功率激光薄膜元件目前面临着能够运行在更高损伤阈值、更高重复频率和更高稳定性等一系列更严峻的挑战，其中不仅涉及薄膜单脉冲激光辐照下的抗激光损伤能力和多脉冲辐照下的损伤生长现象，也包括薄膜光学性能和面形精度稳定性引起的激光损伤。本项目拟利用激光冲击波技术作为电子束蒸发沉积薄膜的一种后处理手段，基于其可避免热作用的纯力学行为特点，完成对薄膜中缺陷、膜层微观结构和宏观力学性能的综合改性，以期实现薄膜能运行在更高激光能流并保证长期运行稳定性。主要研究内容包括：完成激光冲击波后处理分别在改善薄膜单脉冲激光辐照下抗激光损伤性能和长期运行稳定性方面的效果表征和机理分析；在实验和理论分析基础上，获得整体性能的优化工艺参数并建立过程模型和多种过程耦合理论。本项目将有望突破现有薄膜抗激光损伤能力提升方法的限制，为促进大型高功率激光装置中薄膜元件向高能量、高精度和高可靠性发展提供一种新的可选方案。

大口径高功率激光薄膜元件目前面临着能够运行在更高损伤阈值、更高重复频率和更高稳定性等一系列更严峻的挑战，打破现有后处理技术的针对性和局限性，探求一种可辅助实现薄膜中缺陷特性、膜层微观结构和宏观力学性能综合改性的后处理技术，对光学薄膜各方面性能的提高和强激光系统连续运行稳定性具有重要的学术意义和工程指导意义。本项目创新性提出利用激光冲击波技术作为电子束蒸发沉积薄膜的一种后处理手段，基于其可避免热作用的纯力学行为特点，探讨其对典型基频薄膜元件中缺陷、膜层微观结构和宏观力学性能的影响过程，并完成了激光冲击波后处理分别在改善薄膜单脉冲激光辐照下抗激光损伤性能和长期运行稳定性方面的效果表征和机理分析。结果表明，在合适的激光冲击参数下，激光冲击后处理对基频高反膜和减反膜的抗激光损伤能力均有明显提高，且激光冲击后处理对薄膜固有缺陷和膜层结合力等力学性能的综合改善是薄膜抗激光损伤能力提高的主要原因。同时，激光冲击后处理通过对薄膜堆积密度与表面粗糙度的协同竞争作用，影响着薄膜的水吸收和长期运行稳定性，目前研究结果发现激光冲击后处理仅对基频高反膜水吸收的降低有积极作用，而对基频减反膜水吸收基本没有改善。建立了激光冲击总压强修正方程，证实了临界总压强的存在，为优化工艺参数的选择提供了理论依据。这些结果充分证明激光冲击强化技术作为一种光学薄膜后处理技术，对光学薄膜各方面性能的提高是可行的，将有望突破现有薄膜抗激光损伤能力提升方法的限制，为促进大型高功率激光装置中薄膜元件向高能量、高精度和高可靠性发展提供一种新的可选方案。