| With the development of modern optical technology, more and more large aperture optical systems are applied in astronomical optics, space exploration and the laser Inertial Confinement Fusion (ICF). Because of the large aperture aspherical element has advantages of expanding the field, improving the spatial resolution, reducing complexity of the system, increasing the signal energy, and so on, it becomes a key component of large aperture optical system. But the processing precision of aspheric optical element is restrained by its surface shape detection accuracy, so it has become one of the key factors restricting the widely use of the large aperture aspheric element, and it is very important to detect the surface of the large aperture aspheric element. In order to study the surface shape error detection of the large aperture parabolic element, a new sub-aperture stitching measurement technology based on aberrationless theory is proposed in this paper. The advantages of this method include that the large aperture reference component is unnecessary, the freedom during the movement of sub-aperture is reduced, the difficult of the sub-apertures’nominal motion path calculation and positioning is reduced, the vertical measuring range is increased, and the lateral resolution is improved. The research work of this paper as follows:Firstly, the interferential detection principle of sub-aperture stitching is introduced, and the circular sub-aperture stitching method and annular sub-aperture stitching method are discussed. The annular sub-aperture stitching can only extends the longitudinal dynamic range of the interferometer, and the adjustment and calibration of circular sub-aperture stitching detection device are more complex and difficult. According to those defects, a new sub-aperture stitching method is proposed in this paper, the calculation method of sub-aperture nominal motion path and the solving method of object space coordinate of sub-aperture discrete data point are intensively discussed; the principle of stitching between two sub-apertures and local average error stitching algorithm are compared; the advantages and disadvantages of the two methods are analyzed; the objective function global optimization stitching algorithm based on the weight coefficient is confirmed.Secondly, the accuracy and repeatability of the objective function global optimization stitching algorithm is simulated by MATLAB; and the global optimization stitching algorithm programs are written; the simulation are compared and analyzed. The results show that the objective function global optimization stitching algorithm based on the weight coefficient and the proposed method in this paper both have high accuracy and good feasibility.Finally, The ZYGO interferometer and reconstructive five dimension frame are used to detect the surface error of a150mm diameter parabolic using sub-aperture stitching method. At last, the experimental difficulties and the error of actual stitching experiment are analyzed. |
