Research On Optical Interference Testing For Optical Aspherical Surface

Aspheric optical elements are important role in improving image quality, reducing weight, improving optical properties, simplifying the structure, reducing the workload of assembly, shorten the development and production cycles, lower cost. Aspheric optical system has been more and more used in these fields, such as aviation, aerospace, military, information, photography and so on.Aspheric optical system must contain one more high-precision aspherical surface. A complete aspherical manufacturing technology includes two parts:the precision processing and testing technology. Although aspherical lens is much better than spherical lens in the performance, but it is much more difficult than the spherical in processing and testing due to its complex surface shape, which are two big problems for application wildly for a long time. Currently, there are already some ways to test aspheric, but there is not a good method, which is good universal property, easy use, high precision and low cost, so researchers are still exploring.Some methods of aspheric testing are compared with their advantages and disadvantages, and have been deep studied on phase-shifting shearing interferometry, ZYGO interferometry and zone plate interferometry, and give research results in this paper. The main works we have done as follows:1. A set of inspection device with lateral shearing phase-shifting interferometer for optical aspheric surface has been developed through combination of "10th five" research plan project, including a test device, four standard lens, a set of test software. The testing accuracy of this device is less than λ/10, and with domestic advance level and patent also.The experiment for parabolic aspheric surface, which is diameter110mm and vertex radius of curvature960mm, was done with this device, and the measurement error is PV=0.43λ. and RMS=0.01λ.The error analysis was done for phase shifting technology. At first, the phase shifter has been calibrated by Wavelet digit filter and Fourier transform, and the calibration accuracy is0.39%; then compensating algorithm for phase shift was presented, which based on combination of four phase shift and Fourier transfom, and the error is1/100λ.2. Based on ZYGO interferometer, the direct testing method obtaining the aspheric surface error has been studied by wave subtraction. This method is different between idea wavefront from calculation and testing wavefront from ZYGO interferometry, and the error is reduced with surface absolute measurement technology. For parabolic aspheric surface with diameter300mm and vertex radius of curvature2500mm, the measurement error is PV=0.16λ and RMS=0.03λ, and is verified by autocollimator method.3. The common path interference system based on zone plate interferometry is designed and built. The processing algorithm for interference fringe, which based on coordinate transform, is developed. For the hyperboloid with radius of curvature of103.26mm and diameter of40mm, the measurement error is PV=0.38λ and RMS=0.05λ, and the result is verified with Taylor-Hopson profiler.