Application Of Phase Diversity In Piston Detection Of Segmented Telescope

For segmented telescope, rearranging sub-mirrors to an ideal surface or achieving co-focus and co-face is extremely important. In practice, the co-focus is easier to achieve but not the co-face.It is very hard for ordinary wave-front detection methods such as Hartman method, shearing interferometer method and curvature sensor method to detect the piston difference between sub-mirrors of segmented telescope, because they are very complicated in configuration and insensible to the piston phase. On the contrary, phase diversity method need fewer configurations and can be used to piston detection in very high resolution. But phase diversity is not perfect, and it will need a lot of calculation in wave-front detection, so it is very hard to be used in real-time wave-front detection. Based on the basic theory of phase diversity, a simulated experiment on computer and a simulated segmented experiment in laboratory have been performed, and some desirable results achieved.In the first section, some basis wave-front detection methods and the history and current situation of phase diversity have been discussed. In the second section, the basic theory of phase diversity has been discussed in detail, including the form of objective functions under Gaussian noise and Poisson noise and the derivative form of objective functions to the unknown variables. In the third section, some local and global optimization algorithms have been proposed. In the forth section, the simulated experiment on computer and the simulated segmented experiment in laboratory have been discussed, the experiments can prove that phase diversity can be used to piston detection in very high resolution, the error in detection can be less than 25nm or even less. At last, a summary has been made and a prospect has been proposed.