Wavefront Sensing Of Extended Object Based On Phase Diversity Method

Due to the disturbing effect of airflow, the refractive index of air varies randomly,it will disturb the wavefront of light when passing through the atmosphere. Thuscould significantly affect the imaging quality of the optical detection system andlimits the resolution of the optical system. Adaptive optics technology can overcomethe influence of wavefront distortion effectively, greatly improve the resolution ofthe imaging system, has been widely used in the correction of wavefront distortioninduced by atmospheric turbulence. Adaptive optics technology consists of threeparts, wavefront sensing technology, wavefront control technology and wavefrontcompensation technology. Traditional wavefront sensing technology, such asshearing interferometer and the Shack-Hartmann sensor, needs a natural guide staror an artificial laser guide star as reference light for wavefront sensing. However forextended targets, such as nebula and sun, the traditional wave sensing technology isno longer applicable.The basic idea of phase diversity wavefront sensing technology is that usingfocused and defocused images collected at the same time to restore the pupil phaseof wavefront distortion caused by air turbulence, but also can be used as apost-processing method to recover the target image. Phase diversity method has nospecial requirements on the target, not only for the point target, but also for extendedtargets. Compared with the traditional wavefront sensing technology, the opticalhardware requited by phase diversity method is simpler and easier to implement,there is the advantages of non-common path errors. With the improvement ofcomputational hardware and algorithms, the phase diversity method has become animportant development direction in wavefront sensing technology.The main contents are given as follows:(1) On the study of atmospheric turbulence characterized by Kolmogorov theory,a random wavefront that meets the atmospheric turbulence characteristics issimulated using Zernike polynomials.(2) By studying the theory of phase diversity method, achieve the numericalsimulation experiments. Phase diversity is to use focused and defocused imagescollected at the same time to restore the pupil phase of wavefront. By theconvolution of the objective function and the point spread function, we can simulatethe imaging process of a linear space invariant imaging systems. In order to solvethis process an object functional is required. Then we can estimate the unknownpupil wavefront phase by L-BFGS optimization method. (3)Considering the retrieval accuracy will be affect by system errors, we analysisthe effects of some errors by numerical simulation. Results show that the systemitself aberration, defocus error, position error of the focal plane, alignment errors offocused plane and defocused plane, image noise and other factors impact onwavefront recovery algorithm. Different methods are presented to reduce theseerrors for different error factors.(4) A tested experiment is built to validate the fact that phase wavefront detectionmethod is effective. For point and extended targets，the structures of experimentalsystems are different. In the situations of static aberrations, we analysis thewavefront recover ability of phase diversity.