基于双回转相位板的复杂面形拼接测量理论与方法

Complex surface shapes such as large convex aspheres, cylinders and free-form surfaces are finding increasingly more applications in optical systems including large telescopes, lithographic lens and inertial confinement fusion systems, serving as important components with direct influence on the system performance. Hence they have to meet strict demands for the high-middle-low frequency surface errors. Traditional approaches typically including the null test now encounter a bottleneck due to their very limited measuring aperture, insufficient aberration compensation or low accuracy, which significantly blocks the promotion of manufacturing quality. We first propose a novel method combining counter-rotating phase plates and subaperture stitching, which is promising to break through the bottleneck of limited aperture in null test and limited aspheric departure in subaperture test. The phase plates as near-null optics are able to generate variable aberrations, making the method flexibly applied to complex surfaces of various shapes while possessing the advantages of compact design, single adjustment degree of freedom, easy calibration and alignment, and absence of circular pupil distortion. A novel stitching model is also proposed in combination of ray tracing and configuration space theory, in order to precisely separate the surface error from the aberrations induced by misalignment of the test surface and the near-null optics. We are focused on the key problems including the near-null optics design, and the principle and algorithm for near-null subaperture stitching. We finally aim to develop a subaperture stitching interferometer prototype for complex surface shapes.

大口径凸非球面、柱面甚至自由曲面等复杂面形在大型望远镜、光刻物镜、惯性约束聚变等光学系统中的应用越来越多，是直接影响系统性能的重要元件，其高、中、低频面形误差要求都很苛刻。以补偿检验为代表的传统方法，存在测量口径受限、像差补偿能力不足或精度不高等技术瓶颈，严重制约其制造水平的提升。项目首次提出双回转相位板的近零位补偿与子孔径拼接相结合的新方法，突破传统补偿法的口径受限和子孔径拼接法的可测非球面度受限的难题，利用双回转相位板产生可变的像差，可灵活适用于不同形状的复杂面形，具有结构紧凑、调整自由度少、易于校准和对准、无圆形孔径畸变等突出优点；首次提出光学追迹与位形空间理论相结合的子孔径拼接优化模型，准确分离面形误差与近零位补偿器或被测镜失调引入的像差。项目重点解决双回转相位板的光学设计、近零位补偿器的光机设计以及近零位子孔径拼接原理与算法等关键问题，并研制复杂面形的测量装置样机。

测量是制造的前提。大口径凸非球面、柱面甚至自由曲面等复杂面形在大型望远镜、光刻物镜、惯性约束聚变等光学系统中的应用越来越多，是直接影响系统性能的重要元件，其高、中、低频面形误差要求都很苛刻。上述复杂光学面形应用受到极大限制的主要技术瓶颈在于面形的超精密测量，传统干涉测量无法适用的根本问题在于干涉仪的动态和横向测量范围非常有限。项目发明了像差可变的近零位补偿器，突破了传统补偿法的口径受限和子孔径拼接法的可测非球面度受限的难题，创新拼接优化算法，解决误差解耦难题，拓展出复杂面形的可变补偿拼接测量方向。首次提出双回转相位板的近零位补偿与子孔径拼接相结合的新方法，利用双回转相位板产生可变的像差，可灵活适用于不同形状的复杂面形，获美国专利授权；首次提出光学追迹与位形空间理论相结合的子孔径拼接优化模型，准确分离面形误差与近零位补偿器或被测镜失调引入的像差，将传统算法要求的微米级空间精度放松到亚毫米级。项目重点解决了基于双回转相位板的近零位补偿器设计、近零位子孔径拼接建模与算法设计等关键问题，研制的拼接测量装置样机达到或优于预期指标。项目首次实现了300mm以上口径凸非球面的近零位拼接测量，并推广应用于上海天文台望远镜改正镜组的面形检测，其中凸球面最大测量口径506mm，是迄今公开报道的拼接测量凸面口径最大、R/D最小的应用实例，为相关应用单位开展空间红外相机和大口径望远镜的研制提供了光学检测技术的有力支撑。项目成果被国际同行评价为“国际公认的贡献”，是“过去十年子孔径拼接测量非球面取得的最出色进展之一，并且无疑是精密光学计量界的扎实的贡献”。