Fabrication and testing of a 600mm diameter brazing SiC mirror

SiC is a preferential material for space large aperture mirror at present. Aperture of 1 meter sic mirror can meet most requirements of space optical systems. For larger aperture sic mirror, it is not economical and safe to make the monolithic body directly. The SiC mirror brazed assembly with several segments can solve these problems. In this paper, one Φ600 mm sic plane mirror as demonstration welded with 3 radial segments is roughly grinded to the required figure at first, then the mirror is finely grinded and polished by CCOS technology, the RMS of the figure error is less than 1/20λ (λ = 632.8nm) finally. The problems of the preferential removal near braze joint and material removing rate influenced by deformation of mirror surface are solved. Methods of reducing the residual stress of mirror are discussed. At last, some measurements and experiments are carried on, and the results conclude that the brazed SiC mirror can meet the requirement of large aperture optical systems.