太阳CO 4.66μm光栅光谱仪的光学设计

Optical design of grating spectrograph for solar CO 4.66μm spectrum observation

为了实现对太阳中红外光谱CO 4.66μm波段的观测,设计了一台光谱中心波长为4.667μm的高分辨中红外光谱仪。基于科学观测需求分析了光谱仪的技术指标,为降低红外仪器的背景辐射,光谱仪整体置于真空制冷环境中;为达到高分辨率的观测需求,采用中阶梯光栅作为分光器件;为获得更优的像质,同时达到压缩光路的目的,光谱仪采用李特洛结构与离轴三反消像散技术相结合的光学设计,离轴三反同时承担了光谱仪中准直和成像的功能。在同轴三反系统的几何光学成像理论的基础上,研究了同轴三反结构、离轴三反结构以及光谱仪结构的求解和设计优化方法。光谱仪的焦距为1 300 mm,数值孔径为0.035,视场为20.3'×0.158',系统的整体尺寸小于700 mm。结果表明,在工作波段范围内,光谱仪点列图的均方根直径小于5μm,能量集中于一个像元尺寸范围内,光谱仪系统设计结果满足要求。

To meet the requirements of the solar mid-infrared spectral band CO 4.66-μm spectrum obser⁃vations,a high-resolution mid-infrared spectrograph with a 4.667-μm central wavelength was designed.First,the technical indicators were studied based on the requirements of the scientific observations that have to be made.The entire spectrograph was put in a vacuum liquid-nitrogen refrigeration vessel to reduce the background radiation from the infrared equipment.An echelle is used in the spectrograph as a spectrum splitter to increase the observation resolution.The optical configuration of the spectrograph uses a creative structure by combining the Littrow structure and the Three-Mirror Anastigmatic(TMA)technolo⁃gy.Such a structure provides better imaging quality and optical path compression.In addition,the TMA structure has dual functions,as the collimating and imaging optical paths.The design and optimization methods of the coaxial three-mirror structure,TMA structure,and spectrograph structure were also stud⁃ied based on the coaxial three-mirror system's geometrical optical imaging theory.The designed spectro⁃graph has a size of less than 700 mm,a focal length of 1300 mm,a numerical aperture of 0.035,and a field of view of 20.3'×0.158'.The imaging quality of the spectrograph system was evaluated,with results indicating that,within the working wavelength,the root-mean-square diameter of the spot diagram is less than 5μm,and the energy focuses on one pixel.Therefore,the spectrograph meets the design requirements.