Research On Aspheric Surface Testing Technology Based On Radial Shearing Interferometry

The radial shearing interferometry is a measurement which divides the wavefront with spatial coherence into expanded wavefront and reduced wavefront by a device,and produces interference fringes in its common area.Compared with traditional interferometry,the technology has many advantages,such as common path,insensitivity to external environment vibration and other factors,and wavefront reconstruction by using one interferogram,so it is ready for the development of on-line measuring equipment.This thesis is proposed under the need of high-accuracy testing and fieldwork for aspheric elements,therefore,it is of certain engineering value to study the radial shear interferometry.The main contents of this thesis are as follows:(1)The testing technology of aspherical surface was expounded.And several typical systems of radial shearing interferometer,the theory of optical interference and the wavefront characteristics of radial shearing interferometer were analyzed.(2)The image enhancement technology,space extension theory of interferogram and phase extraction theory based on Fourier transform was discussed,and some issues in phase extraction were analyzed,such as spectrum leakage,filter and phase unwrapping.(3)Based on the wavefront fitting theory of Zernike polynomials,the principle of three methods for solving the coefficient was analyzed.Selected two kinds of different complex wavefronts were simulated,and the relationship between fitting accuracy and fitting order and number of sampling points was analyzed.The results showed that the fitting accuracy by Householder transformation method is higher than the other two methods;for the wavefrontwith different complexity,the higher fitting accuracy can be achieved by selecting the suitable fitting order and the number of sampling points.(4)The theory of wavefront reconstruction based on iterative algorithm was discussed,and its derivation and improvement was carried out.The wavefronts of two different PV values were simulated,and the relationship between reconstruction's accuracy and iterative time,ratio of radial shearing and distortion of the wavefront was analyzed.The simulation results showed that the reconstruction's accuracy of the iterative algorithm can achieve the demands of radial shearing interferometry.(5)According to the testing system for aspherical element designed in this thesis,the experimental equipments were selected.The testing device for aspheric element was built,and a method of fast adjusting optical path was summarized.The same aspheric element was tested by high-accuracy interferometer,which verifies the feasibility of this scheme.