TMT大口径宽角谱介质膜分色镜关键技术研究

High resolution is a key and essential feature of the new generation astronomical telescopes. The current fabricating technology for large dichroic mirrors required in the great telescope systems, such as TMT, has many limitations such as narrow angular spectrum, poor spectral uniformity, which result in a low resolution of the system. With the aim of “see further, see clearer” of the new generation astronomical telescopes, it is essential to make breakthrough in the manufacturing technology of large aperture, wide angular spectrum, and broadband dielectric film based dichroic mirror.This project is aimed at solving the technical difficulties in the manufacture of the dichroic mirrors in the TMT WFOS system. Based on our existing research background of manufacturing, coating and measurement of large aperture planar optical element, new techniques of designing and fabricating the wide angular spectrum dichroic films will be studied. Also novel method of precisely fabricating the dichroic mirror’s substrate with consistent convergence of full band transmission/reflection wave front errors will be investigated. Meanwhile, metrology of the spectral transmittance/reflectance and their uniformities in the large aperture with high resolution and many other key scientific issues will be studied. This project will reveal the controllable rules of charactering and controlling of the wide angular spectrum, low polarization, high steepness, full band surface shape error of the large diameter to thick ratio dielectric film based dichroic mirror, also new methods for manufacturing large aperture dichroic mirror will be established and developed. The fabricated dichroic mirror will satisfy the technical requirement of the TMT WFOS system. This project will provide a solid technical support for the development of advanced astronomical optical system.

高分辨是新一代天文望远镜发展的核心必备特征，当前工艺水平下的介质膜分色镜应用 于以TMT为代表的极大望远镜系统存在角谱范围窄、大口径光谱均匀性差等问题，导致观测分辨率低。新一代天文望远镜实现看的更远、看的更清的建设目标，必需突破大口径、宽角谱、宽带介质膜分色镜制造技术。本项目针对TMT WFOS系统中介质膜分色镜的制造技术难点，基于项目组前期在大口径平面元件加工、镀膜以及相关检测技术方面的研究基础，研究宽角谱分色膜设计方法与性能调控技术、分色镜基板透、反射全频段波前误差一致收敛高精度加工技术和大口径透、反射高分辨光谱特性检测方法等关键科学技术问题，揭示大径厚比介质膜分色镜元件的宽角谱、低偏振、高陡度以及全频段面形误差表征与控制的可控性规律，建立和发展大尺寸分色镜元件制造新技术和方法，实现分色镜元件满足TMT WFOS系统的技术指标要求，为天文先进光学系统发展提供坚实的技术支撑

高分辨是天文望远镜发展的核心必备特征，当前工艺水平下的介质膜分色镜应用于以TMT为代表的极大望远镜系统存在角谱范围窄、大口径光谱均匀性差等问题，导致观测分辨率低。新一代天文望远镜要实现看的更远、看的更清的建设目标，必需突破大口径介质膜分色镜制造技术。本项目针对TMT WFOS系统中介质膜分色镜的技术难点，研究宽角谱分色膜设计方法与性能调控、分色镜基板透反射全频段波前误差一致收敛高精度加工和大口径透反射高分辨光谱特性检测方法等关键科学技术问题，获得以下主要成果：（1）通过研究不同加工工艺去除函数机理，建立多频段误差表征模型，首创磁流变抛光“魔法角度-步距”工艺，建立分段路径卷积分析方法，揭示了路径轨迹及去除函数形貌对中频误差影响机制，提出组合抛光低波纹修形方法，最终获得分色镜基板透反射波前纳米精度光学表面全频段误差控制。（2）模拟了大角度下偏振效应对分色膜波长偏移和过渡带带宽的影响，对比不同折射率比的高低折射率材料对过渡带陡度和反射带共振吸收的影响，提出宽窄带隙组合材料和组合膜堆的初始膜系，将角度、偏振态、透反射率同时作为目标函数，采用全局优化和局部针式优化相结合的综合设计方法，解决了反射带中的共振吸收、过渡带陡度以及通带的波纹抖动难题，建立了新膜系设计方法的理论基础。突破大口径薄膜元件均匀性、应力以及膜厚控制等综合性能调控技术，实现了大口径分色膜的研制。（3）研制了大口径分色膜透反射光谱及其均匀性测量系统，发展了高分辨截止带陡度光谱测量技术，解决了长时间内分束比的稳定探测、大口径范围内光斑随机抖动等难题，最终实现了大口径分色膜透反射光谱及其均匀性的准确测量。本项目揭示了大径厚比介质膜分色镜元件的宽角谱、低偏振、高陡度以及全频段面形误差表征与控制的可控性规律，建立和发展大尺寸分色镜元件制造新技术和方法，实现分色镜元件满足TMT WFOS系统的技术指标要求，为天文先进光学系统发展提供坚实的技术支撑。