| The aspheric mirror because of their excellent properties of optical imaging iswidely applied to many fields, such as in military, in astronomical observation, in ourdaily life and in the health care. With the development of the optical technology, themachining accuracy of aspheric mirror increasingly demanded. There are many differentkinds of aspheric mirrors，and generally speaking, it is time-consuming, costly anddifficult to ensure its accuracy. In precision and ultra-precision machining of aspheric,the aspheric surface testing technology is one of the supporting technologies, becauselevel of accuracy that can be achieved by detecting is often the limit of the machiningprecision. So finding a high precision and a reliable method to detect the non-sphericalmirror is necessary.As a kind of non-contact detecting method of the aspheric mirror surface shape, thelaser shearing interference method, a newer and with higher precision method, isdifferent from the traditional contact-type detecting method and the traditionalinterferometry. The self-interference property of the shearing interferometry makes ithave the unique advantages in testing the aspheric mirror surface shape. Some relatedresearches about the process of using a lateral shear interferometry to measure asphericmirror surface shape have been done in this paper.According to the characteristics of lateral shear interference, some numericalsimulation about the lateral shear interferometry was carried out. Using the four-stepphase shift method of phase extraction and the phase-unwrapping method named basedon segmenting regions containing phase jumps an image processing program waswritten. Also some numerical simulations were done based the program and the errorproblem in the actual processing has been analyzed.The study of wave-front reconstruction algorithms named the coefficientconversion method and the least square method was made with the help of a computer.Both of the two methods are based on the Zernike polynomials fitting. The influence ofthe sampling point spacing, the order of fitting and the changes in the amount of shearon the accuracy in wave-front reconstruction was discussed and a method of dataprocessing error reduction also be proposed.An experiment of using a lateral shear interferometer to measure a parabolic mirrorwas conducted. To solve the practical problems of dealing with later shear interferencefigure, an image preprocessing procedure was presented. The four-step phase-shiftingphase extraction algorithm is verified, and the phase-unwrapping method mentioned hasbeen improved optimization making it more efficient in phase-unwrapping. Byexperimenting, the feasibility of the lateral shearing interference method of testing theaspheric mirror was preliminarily verified. A practical software, can be applied to the lateral shearing interferometric process, was completed in MATLAB environment. |
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