Study On Phase Retrieval On-sit Testing For Lagre Optics

The requirement for large optical mirrors has grown rapidly under the background of many applications such as space detailed survey cameras, laser fusion systems and astronomical telescopes. Large optical mirrors are of special importance to the performance of high accuracy, high resolution and high power in modern optical system. Modern technology meets serious challenge in the manufacture and measurement of these large optical mirrors for their ever-increasing aperture, accuracy and amount.The accuracy and efficiency of optics manufacture depends heavily on the optical measurement technology. The process of large optics manufacturing needs the supporting of on-sit quantitative testing with high accuracy and high resolution. But traditional testing methods cannot meet the requirement of large optics manufacture in many aspects, that has turn out to be a bottleneck to further improving the ability of modern optics manufacture.For exploring a new way of optical measurement, this thesis studies an optical testing method based on phase retrieval, which can serve as a new quantitative on-site testing method to enhance the efficiency of optics manufacture. Phase retrieval is a wavefront sensing method that utilizes intensities to reconstruct the phase of optical field. As an optics testing method, phase retrieval has the advantages of simplicity, adapting to the on-site environments and suiting for quantitative calculation. So phase retrieval has a good application foreground and will be a very effective testing method.The content of this thesis is organized as follows:1. The phase retrieval testing system based on the defocus wave field has been designed according to the theory of classical phase retrieval. The fast computation method for wavefront diffraction is presented which is necessary in phase retrieval algorithm. The multi-images phase retrieval algorithm is established based on GS algorithm under the theory of projections to constrain sets. The geographic analysis is performed about the converging of this algorithm.2. The sensitivity of the phase retrieval system is studied, and the model that calculates the sensitivity of the multi-planes phase retrieval system is established. Some basic properties of phase retrieval sensitivity are derived. It can be proved that the images close to the focus have higher sensitivity and the phase retrieval error can be reduced with the sensitivity enhanced. The error analysis and reliability analysis with measurement range evaluation are also preformed in details. The error analysis indicates that the accuracy of phase retrieval system can meet the requirement of on-sit testing. The reliability analysis reveals that the bright and dim distribution of images has direct relationship with the high and low distribution of mirror surface shape, which can be utilized as a visualized method to estimate the mirror surface shape.3. The sub-pixel phase retrieval algorithm has been invented to meet the demand of high resolution testing for large mirrors. The principle of sub-pixel phase retrieval has been established, and some numerical experiments are carried out. The influence of noise and off-axis of images to sub-pixel phase retrieval has been studied. The results of sub-pixel study show that this method can significantly improve the testing resolution and brings a new way to high resolution testing. The sub-pixel method as a general idea can also give contribution to other application of phase retrieval where the high resolution testing is needed.4. The phase retrieval method that tests aspheric mirror without auxiliary optics has been invented, which tests aspheric mirror using spherical testing beam. The focusing characters of aspheric mirror under the illumination of spherical testing beam have been studied. The phenomena of"self-interference"together with its influence to the phase retrieval testing have been analyzed. To reduce the"self-interference"due to the aspheric surface, the optimization method has been presented by adjusting the position of point source and shading a part of mirror aperture. A special parallel aspheric phase retrieval algorithm has been designed for aspheric testing and is suit for multi-processors computation. To enhance the compution efficiency of aspheric phase retrieval algorithm, the approximate algorithm using equivalent wavelength has been designed. The location problem of point source and images are studied.The influence of the location error to the measurement accuracy has been estimated for experimental consideration. The mirror shading, which is used to reduce the"self-interference", has been discussed including the mirror shading error and error controlling method.5. To validate the effectiveness of phase retrieval method, many experiments have been conducted including 200mm and 500mm spherical mirrors testing, 250mm spherical mirror testing with sub-pixel method and 175mm parabolic mirror testing. These experiments are performed under the on-sit surroundings. The experimental phenomenon and results are analyzed. The results of phase retrieval kept high compatibility with interference testing. The accuracy of phase retrieval can meet the requirement of computer controlling manufacture. The testing error agrees with the estimation of error analysis.The experiments also show that the influence of surroundings is insignificant and the phase retrieval has good adaptability for on-sit testing.