Research Of Asphere Testing Using Annular Sub-aperture Stitching Method And A High-precision Way To Locate Asphere

The use of asphere in optical system can effectively correct the aberrations, improve image quality and streamline the optical structure. Therefore asphere plays an important role in various fields of astronomy, aerospace, defense and military and so on. In recent years, more and more asphere testing methods appeared, for example, compensating method, calculated holographic method, sub-aperture stitching method and so on. Sub-aperture stitching method is a late-but-fast-developed method; it is of high detection accuracy and good versatility. The main content of this paper is the introduction of the sub-aperture stitching method.In this paper, many problems of the sub-aperture stitching method are discussed and the sub-aperture division formula is derived. The distinguished area of sub-aperture can be determined directly through a new method. In the paper, the referenced sub-aperture is based on the best-fit sphere rather than the vertex sphere. This kind of method can reduce the number of sub-aperture; thereby reduce the complexity of data processing. The stitching method is discussed in detail by a two-sub-aperture-model. Two different stitching algorithms, successive-stitching algorithm and global optimization stitching algorithm are derived and simulated. By the use of MATLAB program, an asphere with50microns asphericity and100mm diameter is simulated to verify the stitching method. The simulation results show that the above method is correct. At the end of the paper, a secondary parabolic with diameter158mm is tested by Zygo interferometer. Compared to the known results, the PV value of the experiment differs about7%and RMS value differs about2%. The stitched surface shape is similar to the known surface shape. This shows that the stitching algorithm is practical.The second part of the paper is talking about a new method to locate asphere by the digital image processing method. This part plays an important role in support of the sub-aperture stitching experiment. The detailed locating method is discussed and an experiment is conducted. The simulation and experiment results both show that the locating method has an accuracy of3-5microns.