在线大口径平面光学元件面形高精度检测的方法研究

For the lack of an instrument with high accuracy to measure the surface error of an on-line optical flat element with large aperture, phase measuring deflectometry(PMD) is proposed to achieve high accuracy surface error measurement for an on-line flat optical element with large aperture because it provides a contact-free, high dynamic range, high sensitivity, full field metrology method with easy system setup and alignment. In this proposal, the system design and related theory are suggested firstly. For examples, the camera lens is designed to have the aperture stop as the first surface, and the screen and the test flat are parallel with each other. A method for the high accurate calibration of the coordinates of each reflection point on the test flat will be studied deeply. And we will separately research the reconstruction algorithm for the unequal-interval zonal method and how to eliminate the effect of parasitic reflection on the deflectometric measurement of optical flat element surface figure. Secondly, the main methods of controlling the global surface error are studied. A shearing self-calibration algorithm and a method of guiding to align the test flat and the screen, which are proposed to exactly obtain the system error and reduce alignment error in the PMD, will be studied and be used to achieve a high accurate measurement for the low order terms in the test flat. Thirdly, a stitching process is required for measuring optical flat element with large aperture on line. The stitching calculation method for the slope data on a square sub-aperture and the rules of stitching error propagation is deeply researched. Finally, a multi-camera PMD setup, which is used to measure the surface error of an optical flat element with large aperture and 45 degree tilt, is built in our lab. This hardware system will achieve an accuracy with 1/5 wavelength (PV value) for a 400mm×400mm square flat element. The scalar and vector Zernike polynomial on the unequal interval sampling which can be used to reconstruct surface without integrating error and analyze the coefficients without coupling and aliasing is developed. Therefore, the research not only can provide a new way for us to measure the surface error with high accuracy for an on-line flat element, but also provides a scientific knowledge for the improvement of the beam quality of a laser system with high power output and the image quality of an imaging system. Also, it will provide a scientific guidance for optical system alignment and optical components in their manufacturing process. And the research can play an important role for us to understand the gravity effect on the variation of the surface figure of an on-line flat element.

针对当今在线大口径平面光学元件面形高精度检测的困难与需求，申请人提出了相位测量偏折术实现在线大口径平面光学元件面形高精度检测的方法研究课题。本项目拟开展：PMD大口径平面光学元件面形检测的光路结构设计与相关理论研究；其次，PMD平面元件检测的全局面形误差主要控制方法研究；第三，子孔径斜率拼接算法及误差传递规律研究；最后，对大口径平面元件面形在线高精度PMD检测平台进行设计，加工、建立大口径平面光学元件45°倾斜时的多相机子孔径拼接PMD面形检测硬件平台，使重力环境下被测口径400mm*400mm平面元件的全局面形达到1/5波长的检测精度（PV值）。因此，该课题研究可为在线大口径平面光学元件面形高精度检测提供新方法，也可为大口径高功率固体激光系统的光束质量和成像系统的像质改善提供科学依据，以及光学系统装校和元件加工质量控制提供指导，并为重力如何影响元件面形一般规律的探究奠定基础。

本项目进行了基于相位测量偏折术的在线大口径平面光学元件面形高精度检测研究，建立了相位测量偏折术在线高精度检测的相关基础理论和方法，并设计、加工和搭建了多相机拼接大口径元件面形检测硬件平台。取得了如下重要成果：1.建立了相位测量偏折术检测平面光学元件的基本理论，得到了反射点坐标获取方法和透明元件后表面反射影响去除的方法；2.建立了系统模型并进行了各参数系统误差灵敏度分析，提出了低阶系统误差控制与扣除方法；3.提出了双目立体子孔径拼接偏折术检测算法和实现了拼接误差控制的高精度检测；4.研制了六相机子孔径拼接的在线大口径元件相位测量偏折术检测平台，有效测量口径可达400mm×400mm，检测平台可满足45度倾斜下平面元件的高精度检测需要。项目组共发表论文33篇，其中SCI论文22篇，申请国家发明专利13件，其中授权7件，培养4名博士研究生，15名硕士研究生。