Challenges and strategies in high-accuracy manufacture of the world's largest SiC aspheric mirror

Abstract In consideration of the difficulties in the high-accuracy manufacture of the world's largest aperture SiC (silicon carbide) aspheric mirror, such as the difficulty of processing complex mirror blanks, low accuracy and efficiency of conventional processing, print-through effect, inconsistent processing and testing states, high stress/poor denseness of conventional cladding, the insufficient dynamic range of conventional measurement, and air turbulence of long optical path testing, we proposed the water-soluble room temperature vanishing mold and gel casting technology, homogeneous microstructure reaction-formed joint technology, nano-accuracy efficient convergence processing technology, gravity unloading technology, high-denseness low-defect PVD (Physical Vapor Deposition) cladding process, data fusion testing technology, time-domain averaging method, etc. On the basis of the proposed key technologies and methods, we have currently developed the world's largest SiC aspheric mirror with the size of ⌀4.03m. The impressive performance of the SiC aspheric mirror is verified as follows. The area density of the SiC blank is less than 120kg/m2; surface error testing accuracy is less than 6nm RMS; the thickness inhomogeneity of cladding layer is less than 5%; the final surface error and roughness are 15.2nm RMS and 0.78nm RMS, respectively.