The Co-Phasing Detection Of Segmented Mirror

The angular resolution of telecope is influenced by the intensity of atmospheric turbulence,the aperture of telescope and the wavelength of observation and so on.If the influence of atmospheric turbulence is ignored and the operating wavelength is fixed,the aperture of telescope has to be larger to explore the objects which are more distant and faint.To realize this goal,one of the most important development trend is segmented mirror.However,it also bring new puzzles,one of which is the detection of piston error.Only the segmented mirrors satisfy the requirement of co-focus and co-phasing,can it reach the same angular resolution with an equivalent single mirror.This paper investigates the problems of the detection and maintainment of co-phasing in detail,and proposes a new method to detect piston error.Also,to verify the feasibility of the method,some experiments are carried out and good results have been achieved.The contents are as follows:Firstly,the effect of segmented errors to to telescope imaging is analyzed by the technology of Fourier optics,and the relationship between segmented errors and strehl ratio is analyzed.All the results we get are verified by numerical simulation with MATLAB.Secondly,to detect the piston error,a new method which combines the broadband phasing with dual-wavelength technology is proposed.This new algorithm is analyzed according to the circular aperture diffraction.Then we get the relation between bandwidth and measurement range as well as the relation between measurement wavelength and range.All the reationships we get are verified by numerical simulation with MATLAB.At the same time,the influence of sub-aperture synthesis error for imaging quality is analyzed,such as the eccentric error,the clearance error and the CCD noise.Finally,the experiment system of co-focus and co-phasing of segmented mirror is built in lab.To achieve the confocal of segmented mirrors,this paper adopts the method which is based on the desity and contrast of interference fringe to adjust the larger defocus and tilt error with manual operation,and the method which is based on the active optics and Shack-Hartmann wavefront sensor to correc the smaller defocus and tilt error with automatic operation.Also a structural support of segmented mirror is designed and verified by simulation.It's concluded that the support structure can well meet the requirement.The result of co-phasing is verified by the technology of fringe tracing.