Development of High-Quality Light-Weight Mirror for thr Space-Borne Cooled Infrared Telescope

点击翻译按钮获取中文摘要

We fabricated a spherical mirror of 150mm in diameter, which was made of SiC (silicon carbide) as a test mirror for the space-borne light-weight cooled telescope for the infrared use. The optical tests of the mirror indicate the distortion of the mirror at low temperatures (<200K). The amount of the distortion was, however, 0.6mum peak-to-valley at most, and we attributed it to the bi-metal effects produced by the difference in the thermal contraction between the CVD SiC on the surface and the porous SiC of the core. We did not detect very large distortions due to SiC material itself, which shows a quite contrast to the metalic mirrors. The porous SiC has a specific weight of 2 g cm^<-3>, which is quite advantageous for light-weight mirrors of space-borne telescopes. The CVD SiC is required to obtain high-quality polishing. The distortion was reproducable and we concluded that it could be reduced to a negligeble level if we could have a sufficient accuracy in figuring the SiC blank of the mirror. The present investigation showed that SiC mirrors are very promising for the light-weight mirror for space-borne cooled telescopes in future, but we still need to improve the blank processes to achieve the goal.