Study On The Treatment Of The Surface Defects Of PVD Modified RB-SiC Mirror

With the rapid development of space optics, the spatial mirror apertureconstantly increases in order to meet the requirement of high optical resolution. Themirror has to be lightweighted as much as possible while the optical and mechanicalproperties are maintained. SiC is a kind of new material for special mirrors anddeveloped rapidly in recent years. Compared with some advanced countries, SiCtechnology is still young in China. Many problems had been encountered due tolacking practical experience. This paper focuses on the surface defects of PVDmodified RB-SiC mirror during the finishing stage. The treatment methods arediscussed based on the analysis of formation mechanism.The background and recent technical status of SiC mirror at home and abroadare described. The mathematical model of impact on the large crystallizationparticles in modified layer for different technologic parameters is established basedon Preston equation and technical ability of the laboratory. The technologicparameters include hardness of polishing lap, granularity of polishing material,relative pressure and velocity of polishing lap and mirror. It is hoped to find out theinfluence of the impact force by the parameters acting on the crystallization.The experiments are designed and implemented to prove the mathematicalmodel. The influences of the technologic parameters on the defects of PVD modifiedRB-SiC mirror are analyzed. Based on the result of the analysis, the impact forcemodel is built up. The approaches to estimate surface defects are established throughthe optimization of the technologic parameters. Basically decided that the surface defects are due to the large crystalline peeled off by the unreasonable impact force.Based on the experiments and the theoretical analysis, a set of the PVDmodified RB-SiC mirrors are finished by the optimization parameters. There is nosevere surface defect appeared through the process. The research is helpful mirrorsto control the surface defect during the manufacture of PVD modified RB-SiC.