We propose a sampling method to measure surface roughness of circular flat in this paper. The steps of this method are described in following. First, the number of sampling points is determined based on the radius of the circular flat; then the sampling points are selected by a certain angle in helical line; at last we use instrument like white light interferometer to measure the surface roughness of these sample points. The sampling method can effectively use the surface roughness of sampling points to estimate the surface roughness of the overall optical surface. According to mathematic derivation and simulation analysis, this method has a good sampling results, thus it can be widely used to measure the surface roughness of the circular flat.
Reducing the optical surface roughness is the key to improve the polishing quality of optical mirrors. Traditional
polishing technology in ultra-smooth polishing glass has been used widely for a long time. In this paper, the theories of
traditional polishing in polishing process were summarized. The problems in polishing procedure were analyzed and the
influence factors of optical surface roughness were provided according to the polishing procedure of optical mirrors, and
the relative measurements were pointed out. During the factors, polishing slurry and polishing pad are the important ones.
Contrasting with former traditional polishing technology, roughness factors of new polishing slurry and polishing pad
were analyzed and used in polishing process. The optical mirror of Ø246mm was polished in traditional technology with
new polishing slurry and polishing pad, the obtained testing results were surface roughness 3.421nm before polishing
and 0.613nm after polishing.