The Algorithm Research For Sub-aperture Stitching Test With Aspherics

The interferometers are used to detect large-diameter aspherical mirrors, part ofthem with large apertures are expensive, but the lateral resolution is often insufficient;high-precision ones tend to be smaller, unable to meet the needs of large-diameterdetection. Therefore, Several high precision aspherical detection methods includingOptical Compensation、CGH、Sub-Aperture Stitching have been emerged. While theSub-aperture Stitching method is of the advantages of low cost, high accuracy, and doesnot require auxiliary components. Stitching algorithm is the core of the Sub-ApertureStitching method, research of this assay is very important. This paper is based on theSub-Aperture Stitching Algorithm for testing aspheric surface, including the followingsections:First of all, several aspherical high-precision detection methods have beencompared, and the development of the Sub-Aperture Stitching detection technology hasbeen studied. The circular and annular sub-aperture measurement methods, as well asthe course of development of the stitching algorithm have been emphatically introduced.Secondly, different sub-aperture shapes and stitching modes, as well as variousstitching algorithms of the Sub-Aperture Stitching detection technology have beencompared. Focuses on the introduction of global error averaging algorithm, then basedon the definition of freedom compensation amount and related compensation amount,the fitting principle of reference surface error using Zernike polynomials is clear.Again, a series of pretreatments before the stitching process have been presented.Wavefront fitting pretreatment has been used to remove the bad points of thesub-aperture datas, sub-aperture position transform pretreatment has been used totransform local sub-apertures coordinate systems to the global coordinate system; thentwo tilt removing treatment methods have been introduced.Then, the sub-aperture stitching program has been designed, following a series of sub-aperture stitching simulation analysis for testing aspheric surface has beencompleted. The detected aspherical surface has been fitted using Zernike polynomials,and the analysis of the overlap coefficient, translation error, tilt error, defocus andrandom error on the stitching surface has been finished.Finally, by detecting plane and aspherics using SSI Sub-Aperture Stitchinginterferometer and comparing the stitched surfaces from SSI and stitching algorithm,the stitching algorithm and program’s feasibilities have been verified. The analysis ofthe influence of error in the sub-aperture stitching interference detection system ondetection results has been completed.