为满足空间成像领域对大口径、轻量化、高衍射效率光学衍射元件的需求, 研究了薄膜衍射元件微结构设计及制作工艺。应用Zemax光学软件设计了320 mm口径, F/#100的四台阶薄膜菲涅尔衍射元件, 并利用Matlab软件将连续位相结构转化为离散化台阶分布。研究了薄膜菲涅尔衍射元件的制作技术, 选用透明聚酰亚胺薄膜作为基底材料, 以石英玻璃作为复制模板, 通过多次旋涂的方式实现了厚度为20 μm的衍射薄膜制作。应用Solidworks软件设计并加工薄膜支撑装置。测量复制基板及薄膜对应区域的微结构, 实验结果表明条纹线宽转移偏差小于1.3%, 台阶深度偏差小于8.6%。搭建光路测试在波长632.8 nm处衍射效率平均值为71.5%, 达到了理论值的88%。实验结果表明, 制作的薄膜重量轻, 复制精度高, 并且具有高衍射效率, 满足空间望远镜的应用要求。

For the purpose of fabricating large aperture, light-weighted, and high efficiency diffractive elements, the design of microstructure and fabrication technology of diffractive Fresnel membrane elements were proposed. A 4-step diffractive membrane with 320 mm diameter and F/#100 was designed by Zemax software. The continuous phase distribution was transformed into discrete steps by Matlab software. The fabrication processing chain of membrane diffractive element was studied. Using polyimide film as membrane material and fused silica as substrate, the PI membrane with thickness of 20 μm was fabricated through multi-times spin-coating. The mechanical structure of membrane fixture was designed by using Solidworks software. The measurement results of corresponding position of membrane and glass substrate show that line width errors is less than 1.3%, and the step depth errors is less than 8.6%. The diffraction efficiency in wavelength of 632.8 nm is 71.5%, which is 88% of theoretical value. It can be concluded that the membrane has light weighted structure, high replicated accuracy, and high diffraction efficiency, which meets the requirement of space-based telescope.