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

制作了直径150mm的碳化硅（SiC）球面反射镜，作为星载轻型冷却红外望远镜的测试反射镜。反射镜的光学测试表明，在低温（<200K）下，反射镜存在畸变。然而，变形量最多为0.6 μ m峰谷，我们将其归因于表面CVD SiC和核心多孔SiC之间热收缩差异产生的双金属效应。我们没有检测到SiC材料本身造成的非常大的扭曲，这与金属反射镜形成了很大的对比。多孔碳化硅的比重量为2 g cm^<-3>，这对星载望远镜的轻型反射镜是非常有利的。CVD SiC是获得高质量抛光的必要条件。畸变是可重复的，我们得出的结论是，它可以减少到一个可以忽略不计的水平，如果我们可以有足够的精度在计算的SiC空白的镜子。目前的研究表明，SiC反射镜在未来的星载冷却望远镜的轻量化反射镜中是非常有前途的，但我们仍然需要改进空白工艺来实现这一目标。

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.