Novel Evaluation method of surface figure for large aperture reflecting mirror
TMT GSSMP (giant steerable science mirror prototype) which will be built in CIOMP. The prototype mirror, with elliptical size of 898.5 × 634 (mm), has the function of relaying the beam of light from secondary mirror to different instruments..
The thirty meter telescope (TMT) Project is an international partnership among USA, Canada, Japan, India, China as well as other top R&D nations. The sensitivity and the spatial resolution of telescope will be improved to by far the highest altitude with TMT. Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), Chinese Academy of Sciences, is responsible for the research and development of the tertiary mirror system for TMT. The tertiary mirror system has gotten the new name of giant steerable science mirror (GSSM) because of its unique function and size. The GSSM will be the largest flat mirror in the world with the elliptical-plano figure 3.594 × 2.536 × 0.1 (m), and the first steerable tertiary mirror with such large size. The traditional evaluation method will not be suitable for such large aperture plan mirror surface.
A non-correlation sub-aperture stitching method based on frequency domain was proposed, and the quality of its estimates was analyzed by the project team led by Prof. Xuejun Zhang and Dr. Fei Yang according to their previous work. It is reported in Chinese Optics Letters, Vol. 13, No. 4, 2015.
The TMT GSSM could not only be qualitatively analyzed by this method, but also quantitatively evaluated with NTP (Not To Pass) curve proposed by Lawrence Livermore National Laboratory with a similar method.
The team will build a 1/4 scale prototype of GSSM in CIOMP, and the evaluation method will be applied and verified in the prototype system. The researchers will spare every effort to modify and update the method with more useful features and processes to make sure that it could meet the requirements from the full scale GSSM and some other similar mirror systems.
COL封面故事：大口径平面镜面形分析难题有望解决
图片说明：长光所将搭建的1:4TMT三镜系统原理演示实验平台功能示意。其中椭圆形平面镜面（图中黄色部分，尺寸为898.5×634 (mm)）将来自于TMT次镜系统的光束进行中继，传递至不同的科学仪器终端。
三十米望远镜(TMT)是中、美、日、加拿大、印度等多国合作建造的地面大型光学望远镜，它将把望远镜灵敏度和空间分辨率等技术指标提高到前所未有的程度。中国科学院长春光学精密机械与物理研究所（长光所）负责TMT三镜系统的研制。TMT三镜系统由于其独特的功能特性和几何尺寸，被赋予巨型可控科学反射镜之名。它将以3.594×2.536×0.1 (m)几何尺寸成为世界上最大的椭圆形平面镜，并将是第一个在如此巨大的几何尺寸下具备两维指向可控的反射镜。
传统的面形精度评价方法已经不适用于如此大口径的平面镜系统，如何合理客观的评价大口径平面镜面形精度成为亟待解决的问题。
长光所张学军研究员和杨飞副研究员带领的课题组根据前期工作提出了一种基于频域的非相关子孔径拼接方法作为解决该问题的方法之一，并对其估计质量进行了分析。相关研究成果发表在Chinese Optics Letters2015年第13卷第4期上。
该方法不仅可对TMT三镜系统进行定性分析，亦可采用类似于劳伦斯-利弗莫尔国家实验室的NTP(Not To Pass)曲线给出其定量评价。
今后他们将在长光所搭建1:4的TMT三镜系统原理演示实验平台，对他们提出的评价方法进行实验验证。课题组成员将继续对该评价方法和程序进行修改与完善，确保它能满足将来全尺寸的TMT三镜系统以及类似的大口径镜面系统的技术需求。