KDP类晶体是高功率激光系统中必不可少的激光频率转换光学元件，但由于其在潮湿环境中极易潮解发雾，严重影响了晶体器件的使用寿命，通常需要在晶体表面镀制保护膜来保证它的稳定工作。本项目结合KDP类晶体的特殊性，从溶胶特性和膜层结构的基础性研究入手，探索溶胶合成、微结构控制及其微观、宏观特性与膜层最终性能之间的规律性关系。重点研究晶体表面膜层的低温固化工艺及不同工艺下膜层间的相互渗透、扩散行为和界面层；防潮膜层与减反膜层的应力演变规律及晶体基板与膜层、膜层与膜层间应力释放的有效控制方法。研究薄膜的表面/界面的改善以及膜层的缺陷和应力的降低方法，以提高其激光损伤阈值。通过对减反膜层的微结构调控和表面改性功能化，“钝化”氧化硅颗粒表面从而提高膜层的稳定性。获得高光学性能、耐环境稳定性和高抗激光损伤能力的工艺参数，实现KDP类晶体光学膜的新型复合功能，为高功率激光器倍频晶体元件提供必要的关键技术。

KDP-type crystals, as frequency converters, are essential optical components for high power laser systems. However, it is easy to be deliquesced and fogged in the humid environment, which results in the reduction of working life of the crystals. A moisture-proof coating is therefore, desperately needed to protect the KDP-type crystals. Combined with the particularity of KDP-type crystals, we will start from the fundamental research of sol properties and coating structures, to study the relationship between the sol synthesis, control of the microstructure, micro-macro properties and the final properties of the coatings. This project will mainly focus on the low-temperature curing process and their effects on infiltration, inter-diffusion behavior between different coating layers and the interfaces; stress evolution of the moisture-proof coating layer and antireflective coating layer, and also the control methods of stress release between the coating layer and the crystal substrate, as well as between the different coating layers. To increase the laser-induced damage thresholds of the coatings, we will also investigate the methods to improve the surface/interface of coating layers, as well as those to reduce the defects and stress of coatings. Through the microstructure control and surface functionalization, the surface of the SiO2 particles could be passivated and the structure of the coating would be stabilized. The sol-gel AR coatings with excellent AR efficiency, high environmental stability and laser resistance then could be successfully prepared to achieve the new multifunction for KDP-type crystals, which could provide key technology for frequency conversion crystals for high power lasers.