Measuring The Surface Shape Of Membrane Mirror Based On Shack-Hartmann Wavefront Sensor

Compared with traditional mirrors, a membrane mirror made of flexible film material has the advantages of folding and deployable, lightweight, low cost and etc. It is prospected to be used as large aperture space optical elements. In order to solve the problem of measuring the wavefront of the membrane mirror, a method based on the Shack-Hartmann wavefront sensor has been studied in this paper.The significance of membrane mirror and the research status of wavefront measurement are presented, and the Shack-Hartmann wavefront sensing system and the principle of wavefront measurement are introduced firstly. A planar mirror wavefront measurement system and a concave spherical mirror wavefront measurement system based on Shack-Hartmann wavefront sensor are designed and established. Several algorithms for reconstructing the wavefront are researched, including the preprocessing of the light spot image, the determination of the centroid coordination and the algorithm of wavefront reconstruction modal based on Zernike polynomials, and the corresponding programs are built in Matlab.In order to verify the feasibility of the test system and the correction of the algorithms,the wavefront of a concave spherical mirror with a diameter of68mm and a planar mirror made of glass with a diameter of50mm are measured firstly, secondly through the preprocessing of the light spot image from the Shack-Hartmann wavefront sensor and the determination of the centroid coordination,finally the measured wavefront is reconstructed using wavefront reconstruction modal based on Zernike polynomials. Compared with the results of the interferometer, the wavefront errors for the concave spherical mirror made of glass are0.005λ, rms and0.008λ pv (λ=632.8nm), and the wavefront errors for the planar mirror made of glass are0.008λ, rms and0.028λ pv.On this basis, the surface shape of a planar membrane mirror with a diameter of85mm is measured, PV value of the measured the surface shape error is6.825λ, and RMS value is0.682λ. Finally the wavefront measurement errors are analyzed and estimated, including the experimental measurement error, centroid extraction error and wavefront reconstruction error. The thesis provides a means for membrane mirror shape measurement and control.