Study Of Adaptive Optics Technology In Membrane Diffraction Imaging

Membrane diffraction imaging is regarded as the important development direction for large-diameter and light-weighted space-based telescope.However,there are some challenges need to be fixed,such as the zone defects of membrane components caused in manufacture,the deformation of membrane material in space environment,the changes of imaging optical parameters owing to the disturbing in orbit operation,the optical errors introduced in the deployment of space-based telescope,and how to maintain the long-term stability and reliability of imaging optical parameters.A membrane imaging method based on adaptive optics is presented according to imaging wavefront aberrations in this dissertation,that adaptive optics system is the terminal of membrane imaging system to correct the wavefront aberrations and obtain the highresolution image.A high-performance membrane imaging method based on wavefront sensorless adaptive system is put forward according to the facts that the wavefront aberrations of membrane diffraction imaging are almost quasi-static,and the scale of imaging system is strictly restricted.To discriminate the effects on membrane imaging caused by the membrane diffraction component and the correction algorithm,the related studies on membrane imaging with wavefront sensorless adaptive optics are carried out.The studies follow the method that the correction algorithms are firstly discussed in theory,then applied in membrane imaging experiments.The way to advance the studies is from point target imaging to extended target imaging.The studies on wavefront aberrations correction algorithms for point target imaging are introduced firstly to verify correction algorithms and prepare the experiments for membrane point target imaging.A synchronous correction algorithm is presented owing to the limitations of blind optimization algorithms and the general mode correction method for wavefront sensorless adaptive optics.The performance of synchronous correction approach in static and dynamic wavefront aberrations correction is validated by numerical simulations.The dynamic region abstract method is put forward to improve synchronous correction algorithm according to the noise characteristic analysis.Finally,the experiments on wavefront aberrations correction for point target imaging with lens are introduced in detail,the comparative analysis between synchronous correction method and Stochastic Parallel Gradient Descent(SPGD)algorithm is given according to the imaging performance and aberrations correction speed.The experiment results show that the 1.1DL near diffraction limit imaging is obtained by synchronous correction method,and its correction speed is about 4 times that of SPGD algorithm.Then the studies on wavefront aberrations correction algorithms for extended target imaging are introduced to verify correction algorithms and prepare the experiment for membrane extended target imaging.The limitations of SPGD algorithm and modelbased correction approach in image frequency domain are analyzed firstly.Then the theoretical derivation of synchronous correction approach from image space domain is given.The local region abstract(LRA)method is presented to resolve the contradiction between the full-sized sampling for target imaging and the high frame rate demand for adaptive optics.Finally,the experiments on extended target imaging with lens are introduced in detail,the image restoration results of different correction algorithms are analyzed and discussed.The experiment results show that the correction speed of LRA method is about 20 times that of conventional method in static aberrations correction,and the dynamic aberrations correction speed is almost 4 times that of conventional method.The fast-speed convergence of LRA method is beneficial to correct dynamic wavefront aberrations for membrane imaging.The experimental studies on membrane imaging with adaptive optics are carried out,when the algorithm studies and experiment designs are accomplished.The imaging characteristic of typical membrane diffraction component that Fresnel zone plates(FZP)is introduced firstly,and the strong background noise caused by multi-order diffraction propagation of FZP is analyzed.Then the experiments on FZP imaging based on conventional adaptive optics are completed.The improvements and constraints of FZP imaging with conventional adaptive optics are discussed.The experiments on FZP imaging based on wavefront sensorless adaptive optics system for point and extended target are introduced in detail.The correction capability of synchronous correction approach,SPGD algorithm,and LRA method is analyzed and discussed.For point target imaging with FZP,the correction speed of synchronous correction approach is about 4 times that of SPGD algorithm,the 1.1DL near diffraction limit imaging is obtained,and the medium frequency components of MTF are obviously enhanced,which mean that the imaging performance of FZP is evidently improved by wavefront sensorless adaptive optics system.The resolution of extended target image restored by wavefront sensorless adaptive optics system is improved.The convergence speed of LRA method in FZP imaging experiment is about 3 times than that of conventional method.Finally,the preliminary study of extended target image post-processing is introduced.After image post-processing,the background noise of image is removed obviously,and the resolution of image is evidently enhanced.The effectiveness and necessity of adaptive optics system applied in space-based membrane imaging is validated through algorithm theoretical analysis and imaging experiment studies.The results indicate that the real-time wavefront aberrations correction with adaptive optics coordinating image post-processing is an effective method for high-performance membrane diffraction imaging.