Study On On-line Detection Method For Large Aperture Aspherical Surface

With the development of the national defense and tip science technology,more and more large aperture optical systems are applied in astronomical optics,space exploration and the laser Inertial Confinement Fusion.Large aperture aspherical elements play an important role in improving image quality,reducing weight and improving optical properties and so on.But in the process of optical manufacture.the accuracy of manufacture is limited by the surface measurement ability due to its complex surface shape,with the increase need of larger diameter and high precision optical elements,the existing detection techniques can not meet the testing requirements.Therefore,it is the key to solve urgent need of optical components that is to develop an incumbent detection technology and feedback the processing.This dissertation foucus on the online detect of large-diameter parabolic mirror based on the phase shift type lateral shearing interferometry.Lateral shear interferometry is a kind of common path and compared with own interferometry without standard reference wavefront,but due to it’s complex interference fringes,it has important significance and value to study on the wavefront reconstruction method of lateral shearing interferometry.The research on the subject was studied based on lateral shear interferometer wavefront reconstruction method,this paper work as follows:Firstly,the principles of phase-shift lateral shearing interferometry is introduced to get the four-step phase-shifting shear interferogram by MATLAB,then a program was write to simulate its validation.Temporal phase demodulation algorithm was used to solve the wrapped phase,then the surface information can be obtained by the phase unwrapping and Zernike fitting.A parabolic mirror of φ160mm (PV=8.3949λ, RMS=2.3096λ)was simulated,and finally got a surface(PV=9.2150λ, RMS=2.4125λ).Secondly,based on studying the wavefront reconstruction algorithm,according to the principles of phase-shift lateral shearing interferometry, focuses on studing the number of sampling points and the shear displacement size influence on the precision of aspheric surface reconstruction.As Zernike coefficients are orthogonal in the circle,and shearing interference area is not a circular domain;besides for some interference area,sampling points are limited by shears,and also wave information.So this article make a detailed study on selection of effective sampling points and shears.For an computer simulated non-spherical surface to be measured,it’s suitable to set the shearing amount of one-tenth about the size 16mm of the aperture to guarantee high precision,in this case,only 49 discrete sampling points are needed to display the two dimensional surface topography using Zernike polynomial fitting.Finally,the phase-shift lateral shearing interferometry in the lab is used to detect the aspheric surface,the interference figure obtained by the experiment as well as the system error are both analized,and then got the data, that is PV=0.3629λ, PMS=0.0357λ.