Research On Surface Shape Detection Of Coated Mirror Based On Four-step Phase Shift Method

Precision profile detection is a key technology in the field of national defense and aerospace,and has been listed as a key research direction by many developed countries in the world.For example,the panel of Apollo spacecraft uses the coated mirror reflection to realize high altitude thermal control,and the optical design of satellite communication system uses the coated element.In the process of use,the surface shape of the coated mirror element will change due to the action of external forces.By converting the surface shape information of the coated mirror element into the interference fringe image,and then using the computer to process the interference fringe image,the detection of the surface shape of the coated mirror can be realized.However,for the surface shape detection of coated mirror elements,the laser interferometer has large error and low efficiency,so it is difficult to achieve the high precision detection requirements.To solve this problem,an interference path based on red LED light source is proposed in this paper to realize the conversion of surface shape information of the coated mirror.Combined with the four-step phase shift method and the Zernick polynomial fitting method,a surface shape data processing algorithm with improved unwinding phase is designed to restore the surface shape of the interference fringe image.By improving the image quality of the interference fringe and the accuracy of the unwinding phase,To improve the accuracy of surface shape detection.The specific research work of this paper is as follows:An interference path based on red LED light source is designed,and the polarization interference signals in the path are analyzed.The interference path is simulated by using Zemax simulation software to verify the reliability of the interference path.After simulation,the interference optical path is built on the experimental platform.Aiming at the difficulties in the algorithm of surface data processing,this paper firstly extracts the phase information from the interference fringe image by the four-step phase shift method,and obtains the winding phase diagram.Then,an improved phase unwinding algorithm is designed to unwrap the winding phase graph,and residual handicap is introduced to improve the effect of phase unwinding.Finally,the phase information contained in the unwinding phase diagram is fitted into the 3D profile data by using the Zernick polynomial fitting method.The profile data is finally given in the form of PV value,RMS value and profile restoration map.In order to verify the change rule of the surface shape of the coated mirror under the action of high intensity laser,the finite element analysis of the surface shape change rule of the coated mirror element was carried out by ANSYS simulation software.The results show that the coated mirror will deform during the application process,and the coating surface shape detection method proposed in this paper has practical research value.The experimental verification of the proposed detection method shows that the interference fringe pattern detected by the interferometer is seriously affected by parasitic fringe and speckle,and the detection error is large.The proposed detection method is more suitable for the detection of the surface shape of the coated mirror.