Point Diffraction Interferometric System For Spherical Surface Testing

Optics with spherical surfaces has the advantages of ease to fabricate and low cost, and it is widely applied in modern precise optical systems. The development of the high-tech frontier fields such as microelectronics, aeronautics and asreonautics, has placed ultra-high requirement on the precision of optical surfaces, and so does the measurement tools. Since the achievable precision of traditional interferometers for testing spherical surfaces, such as the Twyman-Green-type and Fizeau-type interferometers and absolute measurement technology, is limited by the aberration of standard optics that produces spherical reference wavefront, they cannot meet the needs of high-precision spherical surface testing. As a novel precise measurement tool, the point diffraction interferometer (PDI) enables the measurement precision in the order of subnanometer, and has good precision reproducibility. It is a significant research focus on the high-precision optical surface testing filed. However, the domestic research on the PDI is at the starting stage, and there are still many key technical issues to further study and problems to solve.This dissertation mainly research on the pinhole-type point diffraction interferometric system for the high-precision testing of spherical surfaces, including precise modeling analysis of pinhole diffracted wavefront, accurate calibration of testing system error factors, experimental data measurement and image processing, etc. The research carried out in the dissertation is of great significance for the high-precision testing of spherical surfaces, especially the high-numerical-aperture spherical surfaces. The major content of this dissertation include:The great contribution of high-precision spherical surface testing technology to the modern optical testing system is discussed. After a review over the current spherical surface testing methods, the necessity of the research on the point diffraction interferometric testing system is put forward.A simulation model based on Finite-Difference Time-Domain method is proposed to precisely analyze the pinhole diffracted wavefront. The related factors to the sphericity of diffracted wavefront, such as the pinhole thickness, diameter, numerical-aperture range and the incident wavefront error, is analyzed in detail. And the simulation results provides theoretical basis for the related devices design in the point diffraction interferometric testing system.A pinhole point diffraction interferometric testing system and the design scheme are proposed for high-precision spherical surfaces testing. Combined with the practical application, the design of key technologies and devices, as well as the corresponding basis is described in detail.The end rotation of the PZT phase shifter in interferometric testing system, as well as its nonlinearity. is analyzed. A technique based on the fringe analysis is proposed for the in-situ testing of PZT phase shifter. According to the changes of the acquired interferograms, the end rotation and displacement of PZT phase shifter are tested in real time, by which the precise control of phase shift in the multiple-step phase-shifting interferometry can be realized. The issue of misalignment aberrations in high-precision spherical surface, especially high-numerical-aperture spherical surface testing is studied, and a rigorous model is presented to analyze the introduced high-order aberrations by misalignment. A novel calibration technique based on the wavefront difference is proposed to calibrate the misalignment aberrations, both the computer simulation and experiments are carried out demonstrate the feasibility of the proposed method.The main error factors of the proposed high-precision point diffraction interferometric system for spherical surface testing, as well as the theoretical model, are analyzed in detail, and the corresponding precise calibration methods are proposed. The achievable theoretical precision of the proposed system is analyzed. The study not only helps to realize the high precision of the testing system, but also provides a feasible way for its further improvement.An experimental, point diffraction interferometric system for high-precision spherical surface testing has been established. The testing experiments for the spherical surfaces, respectively with high and low reflectivities, have been carried out. Compared with the testing results of Zygo interferometer, the accuracies better than0.0100λ PV and0.0020λ RMS are realized. Besides, the repeatability precision of the experimental system is measured, with RMS value better than0.0010λ and PV0.0050λ achieved. The feasibility of the proposed testing system has been demonstrated with the experimental testing results, and some suggestions on the further study are given at the end. This dissertation is of great value for the realization and performance improvement of the high-precision point diffraction interferometric testing system.