Investigation Of Surface-strengthening Technique For Lengthening The Life Of Optical Components Made Of Glassy Material

The optical components made of glassy material have being widely used in aerospace、astronomy、military etc. These components occupy an important position in high-precision optical instruments, such as high-resolution camera、hyperspectral camera、large scale astronomical telescope、intense laser mirror etc. The optical components made of glassy material are very sensitive to the environments, their working stability and working life can influence the performance of optical components directly. Surface strengthening technique (SST) is based on the ductile grinding, combines the chemical etching and physical grinding, to enhance the surface quality and surface strength value. This manufacture technique can reduce the sensitivity to the environments and prolong the working life of optical components made of glass material effectively.According to the manufacture process of optical components made of glassy material, the changes、influences、strengthen modes and evaluation method about the surface strength are analyzed. Focus on the grinding process which concludes the biggest changes of surface strength. Study the birth、development and growth of surface micro-cracks, the removal and testing methods about the micro-cracks are proposed.1、the most important factor influencing the working life of the optical components made of glassy material—the surface strength,is confirmed. According to the analysis about the optical manufacture process, the changes of surface strength are understood. The surface damaged layer and stress concentration in the micro-crack tip are considered as the causes of surface strength decrease, and the direct factor disabling the optical components is the existence of longitudinal micro-cracks.2、the etching method used for the elimination of the surface damaged layer、the release of the stress concentration in the micro-crack tip and the restrain of the longitudinal growth trend are discussed. The micro-crack testing method using molecular colorant is proposed and interpreted; the application of this method is listed.3、According to the analysis about the dynamics of material removal, the main cause for the growth of micro-crack—the normal force Fn is confirmed; study the birth and change of surface compressive stress, and consider the trend of surface strength changes, the conclusion that the max surface compressive stressσ0 performs positive effects on the surface strength is achieved. The ductile grinding mode is advanced:it can restrain the longitudinal growth of micro-crack, increase theσ0 and improve the surface strength. The basic technique requirements of ductile grinding for quartz are: material removal rate≤25um/hr, abrasive size L≤15um. These conclusions have been applied to the surface manufacture of quartz successfully, which is hyperboloid with F1.3、Φ140mm.4、To analyze and study the contents relating the SST, two discoveries are achieved:①the surface roughness has a same change trend with the surface strength;②the chemical properties of abrasive slurry has a great influence on the surface roughness. These conclusions are applied to the manufacture ofΦ240mm light-weighted spherical surface, the result Ra is 0.62nm. According to the surface roughness results of grinding experiments, the basic design requirements for non-imaging surface roughness are concluded.The prediction about the working life of optical components is difficult and complicated, and the SST is only a preliminary explore for the prediction. Although the grinding requirements for ductile grinding are concluded from quartz data, these conclusions are important references for the SST.