大口径超薄凸双曲面镜研制与检测关键技术研究

The rapid development of adaptive optics technology has greatly improved the resolution of ground-based telescopes. Adaptive secondary mirror (ASM) reduces the loss of optical energy and heat radiation of lens group itself inserted, and improve the thermal sensitivity with the wave band in mid-infrared (3 ~ 25um) and the resolution. Adaptive secondary mirror has gradually been promoted and applied on MMT, LBT and VLT and other telescopes based on the above advantages..The development of ultra-thin aspheric mirrors is one of the key technologies of adaptive secondary mirror system. The project proposes innovatively stressed mirror polishing method for convex hyperboloid, combining the special requirements of ultra-thin convex aspheric mirror to the shape, and taking into account the experience and lessons related to the pre-preliminary research. This method will greatly improve polishing efficiency of aspherical mirrors, reduce the residuals of mirror surface shape within high space frequency during development process of the mirrors, and improve the overall optical performance of the adaptive secondary mirror. The project will focus and study on stressed mirror grinding and polishing method of ultra-thin convex hyperbolic mirrors, influence characteristics of mirror thickness uniformity to performance of adaptive correction, the methods of optical test for convex hyperbolic mirror and protection technology for ultra-thin mirrors. Research results can be directly used in upgrading of adaptive optics system of existing 2.16m telescope and others in China, and additivity of secondary mirror for future Antarctic 2m telescope, 10 to 30m level of optical telescopes of China.

自适应光学技术的迅速发展极大地提升了地基望远镜的分辨率。自适应副镜减少了光能损失和插入镜组自身热辐射、提高了中红外波段(3~25um)热灵敏度和分辨率。基于以上优点自适应副镜已逐渐在MMT、LBT和VLT等望远镜上得到推广与应用。.超薄非球面反射镜研制是自适应副镜系统的关键技术之一。本项目结合超薄凸非球面反射镜对面形的特殊要求，并考虑到前期相关预研究的经验与教训，创新性的提出了凸双曲面的预应力研抛方法。该方法将极大地提高非球面化研抛效率、降低镜面研制过程中的高频面形残差、提升自适应副镜的整体光学性能。本课题将围绕超薄凸双曲面镜的预应力研抛方法，镜面厚度均匀性对自适应校正性能的影响特性，凸双曲面镜的光学检验方法和超薄镜的下盘保护技术四方面展开研究。相关研究结果可直接应用于我国已有的2.16m等望远镜的自适应光学系统升级改造以及未来南极2m望远镜、10至30m级光学望远镜的副镜自适应化。

自适应光学作为新兴的技术手段可以很大程度上提高地基望远镜的分辨能力、降低大气湍流导致的星象波前畸变。国外在建的大口径地基望远镜如TMT、ELT等望远镜都有自适应副镜的研制计划。它可减少镜面数量、提高光能收集能力、减少镜面的热辐射、提高红外波段的热灵敏度。其中自适应副镜超薄变形镜的加工是其关键技术之一。.本报告主要包括预应力抛光力学加载原理、光学检测方案的选取和实施（检测方案的设计和优化、公差分析、镜面的加工和检测）、中间尺寸熔石英平板的真空预应力加载试验、微晶玻璃弯月镜的真空预应力加载情况、超薄镜厚薄差导致的影响函数的变化、超薄镜理论展平仿真计算、超薄镜谐振频率仿真分析等内容。现项目中的光学检测方案设计已完成，检测方案中的镜面加工除弯月透镜凹面待镀膜、凸面待抛光外已基本完成，正在进行微晶玻璃厚镜的预应力加载方案的最终验证，后续将进行预应力抛光实验和减薄加工与面形检测。项目集中研究了以下关键技术：（1）支撑均匀性工艺。不均匀的支撑易造成较大非对称面形。本项目探索了各种材料的支撑均匀性情况，选用了较好的支撑方式。（2）各种力学加载模型和支撑方式研究。不同的加载和支撑方式将导致不同的变形分布，进而导致预应力抛光时的比较球面、加载力大小等参数的选择，并且研究人员设计出的支撑方式要经过加载实测、FEA有限元验证等过程才能进一步向下运用。本项目详细深入的研究和对比了不同加载力学模型所产生的变形分布特征，并选取了较合适的加载方式。(3)此外还设计了专门的真空控制系统，用以对部分真空预应力加载提供高精度的真空控制。.自适应副镜超薄变形镜的预应力抛光技术可大为降低确定性小磨头数控加工等技术引起的中高频误差和加工时由支撑引起的印透面形误差，具有优良的面形平滑性。该技术经过发展可应用于我国大口径地基望远镜自适应副镜超薄变形镜的加工上，为超薄变形镜的加工提供一种新的技术和思路。