Studies On The Phase Diversity Wavefront Sensor And Co-phasing Measurement For Segmented Mirrors

For better observing resolution, the developing trend of astronomical telescope isto enlarge the aperture size, whatever on the ground or space. In some certain, theobserving ability for one telescope is always defined according its aperture size.However, better observing results may not be obtained for a larger aperture sizetelescope, and it may not better than a small one due to the influence of atmospheredisturb. So adaptive optics technology must be introduced into telescope system tocorrecte the disturbed wavefront, and the important premise is to measure accuratelythis wavefont aberration. In other hand, the design, manufacturing, machining andtesting suffer unprecedented challenge with the enlarging of telescope aperture size. Theproposal of the segmented primary mirror decrease markedly the weight, cost, periodand volum of telecope, and a super large telescope could be come ture. However, somechallenges are concomitant, and one of the most classic challenges is measuring andcontrolling of the co-phasing error of the segmented primary mirror. With developmentof the larger aperture size telescope, some new wavefront sensing technique and itsapplication in co-phasing testing must be study deeply.Based on above description, we introduce briefly the basic principle and thecorresponding wavefront reconstruction algorithm of phase diversity (PD) wavefrontsensor (WFS). A set of experimental study is also done for continuous anddiscontinuous surface wavefront aberration, and some innovative results have beenachieved as follows:Firstly, some influence factors such as the parameter of image recorder,signal-to-noise ratio (SNR) and defocus distance between the focus plane and defocusplane, which may degrade the measurement accuracy of PD WFS, are analyzed deeply.The analysis results are important for theoretical study and engineering application, andit can direct how to apply in practice and to improve performance.Secondly, we apply the PD WFS for image deconvolution, and the accordingexperimental study is also done. The experimental results show that the wavefront dataof PD WFS can be used to reconstruct the image with wavefront aberration and thereconstructing results have good quality near by the image with diffraction limit. Inaddition, a new structure for PD WFS is proposed based on combinatorial prism, and itcan be applied for the measurement of dynamic wavefront.Thirdly, a modified PD WFS based on the beam splitting principle of a diffractiongrating is proposed to improve the capability of wavefront sensing, such as higher SNR,higher sensitivity and higher measurement capability for high spatial wavefron undertest. Higher measurement accuracy could be achieved for this new PD WFS. Thenumeric and experiment results show that the measurement ability of G-PD WFS is improved obviously, especially for the wavefront aberration with larger amplitude. Thisnew PD WFS may be a better choice for higher accuracy wavefront measurement.Finally, numeric and experimental validation have been done for discontinuouswavefront measurement, such as pistion error and tip-tilt error. Numeric andexperimental results show that the co-phasing errors could be exactly measured by thePD WFS, especially for the co-phasing errors of several segmented mirrors could bemeasured exactly and simultaneously. So that the PD WFS can be used as a co-phasingsensor for the segmented primary mirror.In total, these results and innovations can guide for engineering application, and itcan be used as a unificate wavefront sensor for wavefront sensing in adaptive opticssystem and co-phasing sensing in a common segmented primary mirror telescope. If so,the wavefront sensing system in this segmented telescope can be simplified, and thedata consistency can be assured.