Overview: Gravitational waves are spacetime oscillations radiated outward by accelerating mass objects. Significant astronomical events in the universe, such as the merging of massive black holes, emit stronger gravitational waves. Detecting gravitational waves allows for a deeper study of the laws governing celestial bodies and the origins of the universe, making accurate detection crucial. Gravitational wave detection technology utilizes Michelson interferometers to convert the extremely faint spacetime fluctuations caused by gravitational waves into measurable changes in optical path length. Recently, ground-based large Michelson interferometers have achieved direct detection of high-frequency gravitational waves. However, the detection of low-frequency gravitational waves, which is equally important, is not feasible on the ground due to arm length and ground noise issues. This necessitates the construction of ultra-large Michelson interferometers in space for low-frequency gravitational wave detection. Spaceborne gravitational wave detection telescopes play a vital role in collimating bidirectional beams in ultra-long interferometric optical paths in space. The extremely subtle changes in optical path caused by gravitational waves impose high demands for pm-level optical path length stability and below 10^?10 level backscattered light in these telescopes. The ultra-high level index requirements exceed the precision limits of current ground testing techniques for telescopes. To ensure that spaceborne telescopes maintain their ultra-high design performance in the orbital environment, developing testing and evaluation techniques for these key indicators is a crucial prerequisite for the success of the space gravitational wave detection program. This paper provides an overview of the development of spaceborne gravitational wave detection telescopes, both domestically and internationally. It focuses on the current status and some test results of optical path length stability and backscattered light testing of telescopes under development, as well as further testing plans, providing a reference for the testing and evaluation of Chinese space gravitational wave detection space-borne telescopes.

Overview: In order to achieve the measurement of gravitational wave signals in the millihertz frequency band, the space-based gravitational wave detection projects such as LISA, TianQin, and Taiji projects, which are based on laser interference systems, require the hardware noise floor of the interferometers to be lower than the interstellar weak light shot noise limit. This imposes stringent engineering specifications on the optical-mechanical design and the corresponding interferometer payload. This paper approaches the issue from the perspective of detection mode selection and derives the expressions of readout noise and stray light noise in the interference signal under the single detector mode and the balanced mode. Furthermore, a detailed discussion is provided on the weak-light interference process of the scientific interferometer. The results demonstrate that the balanced mode is capable of suppressing the interference phase noise caused by laser power fluctuations and backscattered stray light across multiple orders of magnitude. However, the suppression capability is constrained by the unequal splitting property of the beam combiner. To address this, a relative gain factor is introduced to compensate for the unequal splitting property of the beam combiner. Further analysis reveals that electronic gain compensation can only eliminate the impact of unequal splitting on one of the two noises rather than both simultaneously. Therefore, a balance must be struck in selecting gain compensation between the suppression of laser power fluctuation noise and stray light noise. Even with this consideration, the balanced mode still offers significant noise suppression capabilities at a magnitude difference, thus potentially reducing the engineering requirements for laser power fluctuations and telescope backscattered stray light.

基于离轴四反的方案设计，从同轴反射系统的理论出发，结合高倍率，低波前畸变，以及高杂散光抑制比等特点对天琴望远镜的原理系统进行了优化设计。实现了在捕获±200 μrad视场内系统百倍的压缩倍率，其入瞳直径300 mm，波前误差优于λ/80。提高三四镜之间光线转折角度进行杂散光抑制，在保证高质量波前的条件下，其三镜的偏角优化结果为5.5°，且三镜为平面镜的引入，降低了后期加工装调的难度。为了对原理系统的加工装调以及杂散光抑制能力进行验证，建立了该系统下0.5倍的缩比系统，实现了缩比系统的波前误差优于λ/175。经公差分析，原理系统有90%的累积概率其波前误差优于λ/40，满足引力波望远镜的指标要求。

由于空间光环境的复杂性，抑制杂散光对保证空间相机成像性能尤其重要，该文针对宽光谱波段成像的空间探测相机光学系统进行杂散光分析和抑制优化设计。通过SOLIDWORKS和TracePro的无损式数据交互建立光机模型，并从光机材料的表面特性、机械结构、镜片透过率等多角度优化杂散光模型，再利用朗伯体光源分别对正反向进行光线追迹，然后结合光机模型的半剖图对系统关键表面进行重点取样分析。分析结果表明：优化后的光机系统在离轴角10.3°~15.4°内，点源透过率值与优化前的系统相比下降了66%~99.4%，在离轴角大于14.2°时点源透过率值接近10^?4量级，在离轴角18.4°处杂散光的点源透过率约为10^?4量级。最后通过鬼像实验，进一步证明了优化后的光机系统设计方法具有良好的杂散光抑制效果。

针对极轨气象卫星FY-3C载荷可见光扫描辐射计（VIRR）在轨红外定标时存在温度反演不一致的现象展开分析，提出了一种全链路自动化仿真分析方法，将仪器结构与卫星轨道参数和卫星平台环境相结合，通过对光机模型的高精度光线追迹来得到杂散光影响的定量化结果。仿真模拟了在轨红外定标和太阳光入射两种情况，确定了太阳杂散光的入射路径，解释了温度反演不一致的原因。将仿真结果与卫星在轨数据进行比对，验证了仿真方法的有效性。该方法可用于同类型载荷的在轨杂散光分析仿真工作，同时也为历史数据的再定标修正提供参考。

针对日冕仪中对杂散光的抑制要求，分析了日冕仪系统中的三种杂散光，包括日冕仪物镜二次反射产生的鬼像点、日冕仪物镜散射点、以及日冕仪孔径光阑衍射光。利用光学建模软件对日冕仪系统进行仿真和分析，发现这三种杂散光的成像位置十分接近且不易区分，并会对系统的检测过程和检测结果产生干扰。根据仿真结果，给出了这三种杂散光的判定与抑制方法，并利用一台视场为±1.08 R_⊙~±2.5 R_⊙（R_⊙表示太阳半径），工作波段为530.3~637.4 nm，通光口径为220 mm，系统总长为4 321 mm的内掩式日冕仪进行了理论验证和实验对比，验证了判定方法的可行性。同时设计了掩体和鬼像遮拦结构对杂散光进行抑制，增加了日冕仪系统杂散光抑制的选择方案，提升了日冕仪杂散光检测的准确率。