LAMOST子镜高反射率反射膜关键技术的研究

According to urgent need to improve the reflectivity of the reflective film of segment of the LAMOST, we propose to study on high reflectivity filmof segment of the LAMOST while the aluminum reflective film currently in use cannot meet the needs of the LAMOST. In accordance with key and difficult points in the study of the high reflectivity film of segments of the LAMOST, we will study on how to control the stress in the multilayer dielectric film of segments of the LAMOST. We will conduct research from three aspects, they are respectively a monolayer film internal stress, the stress between the films and overall residual stress of the reflective film. By controlling the dielectric film growth conditions, we can reduce stress in a monolayer film; through the study on the coupling properties between the different material, we can reduce stress between the films; also, we will establish a new coating design method based on matching the stress to reduce the influence of the residual stress to the surface precision of segment of the LAMOST. The objective of this project is expected to solve the key technical issues about high reflectivity film of segments of the LAMOST, comprehensive guide to select the dielectric material, control the dielectric film growth conditions and design the multilayer dielectric film system. The study will provide technical support to multilayer dielectric film used in the segments of the LAMOST, moreover, it will provides research foundation for study of high reflectivity film in the larger aperture segmented telescope in the future.

本项目根据LAMOST子镜对提高反射膜反射率、稳定性的迫切需要，在当前所使用的铝反射膜不能满足LAMOST需求的前提下，提出了对LAMOST子镜中高反射率反射膜的研究。针对LAMOST子镜高反射率反射膜研究中的重点及难点，对LAMOST子镜介质反射膜的应力控制进行研究。将分别从单层膜内部应力、膜层间应力及反射膜整体残余应力三个方面进行研究。通过控制介质膜生长条件，减小单层膜内部的应力；通过对不同材料间耦合特性的研究，减小膜层间的应力力；通过研究基于应力匹配的膜系设计方法，减小膜系整体残余应力对LAMOST子镜面型的影响。本项目的预期目标是解决LAMOST子镜高反射率反射膜关键技术问题，全方位指导LAMOST子镜中介质反射膜材料的选择、生长条件的确定以及膜系的设计，为介质反射膜在LAMOST子镜中的使用提供技术支持，并为后续更大口径拼接望远镜子镜高反射率反射膜的研究提供研究基础。

本项目根据大口径望远镜反射镜对提高反射膜反射率、稳定性的迫切需求，在目前LAMOST所使用的铝反射膜反射率低、稳定性差的前提下，提出了对LAMOST高反射率反射膜关键技术进行研究。项目主要从应力的角度研究如何在大口径镜面中实现满足LAMOST光谱需求的高反射率反射膜的镀制。研究结合大口径镜面的实际生长情况，充分考虑大口径镜面沉积过程中的折射率不均匀性，分别通过建立工艺参数与薄膜微结构，分析并减小单层膜内部应力；通过界面匹配的方法减小膜层间界面处的应力，从而提高薄膜的牢固度与结合力；通过膜系整体设计优化减小膜系整体应力，减小膜系整体应力对基底面型的改变。项目最终实验在LAMOST准直镜上开展，实验获得的反射膜牢固、不脱落，满足LAMOST全光谱需求，镀膜前后对准直镜进行面型测量，PV值由0.253λ变化至0.3λ，RMS由0.0206变化至0.0239λ，，变化量小，反射膜的光谱和应力对面型的影响均满足要求。项目所研究的内容已经用于LAMOST中，并逐渐将LAMOST光谱仪准直镜中原先膜层替换为项目所研究的膜系，当配有足够大的设备时，项目中的相关技术与方法可用于LAMOST MA、MB子镜中。