空间大口径望远镜紫外到长波红外超宽谱段高反射膜研究

Now space-based telescope is developing toward large aperture and wide working band. The larger the aperture is, the higher the resolution becomes. The wider the working band is, the more abundant information telescope can get. Therefore, large aperture and wide working band mean that space-based telescope can observe more abundant objects under a higher resolution. Because most of the optical systems of space-based large-aperture telescope adopt reflecting configuration, reflecting films coated on mirror substrate determine the working band of telescopes. Metal films are the preferred materials for space-based large-aperture reflecting film coating due to their merits such as high reflection in wideband spectra and low-temperature coating process. However, metal films cannot realize a high reflection in an ultra-wideband spectra from ultraviolet (UV) to long-wavelength infrared (LWIR) region. In this project we propose a design concept of double metal films consisted of thin silver films and thick aluminum films, and multiple UV reflecting-enhanced dielectric films, by which an ultra-wideband optical reflector from UV (250nm) to LWIR (12um) can be achieved through a theoretical design. We will investigate the low-temperature coating processes of proposed compound film structures by using a large-size (2.5m diameter) coating machine, and attempt to prepare the compound films with a high reflection in an ultra-wideband spectra. Furthermore, we will explore the influence of adhesion and protection layers, and promote the environment durability of coated compound films to satisfy the applications under space environment. This project is promising to provide both design concept and key technical reserve for realizing space-based large-aperture and ultra-wideband reflecting film coatings.

目前空间望远镜正朝着大口径、宽工作谱段方向发展，口径越大分辨率就越高，谱段越宽获得的信息就越丰富，大口径宽谱段则意味着空间望远镜能够看得更清、更远、更多。由于大口径空间望远镜光学系统多采用反射式结构，反射镜表面的反射膜决定了其工作谱段。虽然金属膜具有宽谱段高反射、可低温镀制等优点，是大口径空间反射膜的首选，但是无法实现从紫外到长波红外超宽谱段内高反射。本项目提出薄银膜/厚铝膜双层金属膜和紫外反射增强多层介质膜组成的复合膜系结构设计思想，设计出从紫外（250纳米）到长波红外（12微米）超宽谱段内都具有高反射率的反射膜。并采用大口径（直径2.5米）镀膜设备研究复合膜系结构低温镀膜工艺，实验上获得从紫外到长波红外超宽谱段内的高反膜。本项目还将研究连接层对膜层牢固度的影响以及复合多层膜的抗环境能力，获得满足空间环境应用的复合多层膜，为实现我国空间大口径超宽谱段反射镜镀膜提供设计思想和关键技术储备。

针对空间大口径望远镜对超宽谱段高反射薄膜的需求，本项目首先基于传输矩阵理论，利用薄银膜/厚铝膜双层金属膜和紫外反射增强多层介质膜，设计出了从紫外到长波红外全光波段内都具有高反射率的复合膜系结构；其次本项目利用大口径镀膜设备，通过研究薄膜的低温镀膜工艺，在口径大于1米范围内实验上获得了从紫外到长波红外超宽谱段内都具有高反射率的复合多层膜，其中紫外波段250-450nm平均反射率为88.72%，可见波段450-700nm平均反射率为94.81%，近红外到长波红外波段700nm-12um平均反射率为97.88%；最后通过环境适应性研究，在金属层间插入连接层等工艺，获得了满足空间环境应用的复合多层膜。本项目将为实现我国空间大口径超宽谱段反射镜镀膜提供设计思想和关键技术储备，可促进我国全光学谱段空间望远镜的发展，有望应用于大口径空间望远镜中。