Ultra-precision polishing of electroless nickel molding dies for shorter wavelength applications

Electroless nickel is one of the best materials for making optical molding dies, because of its machinability with both single-point diamond turning and polishing, as well as its suitable hardness and durability. This paper deals with the ultra-precision polishing of aspheric molding dies for next-generation hard X-ray telescope mirrors, which require a super smooth surface with a roughness below 0.3 nm root-mean-square (rms). The material was machined using various methods, and a surface roughness of 0.23 nm rms was obtained on aspheric molding dies of 300 mm in diameter. A surface roughness of 0.16 nm rms was achieved on platinum/carbon multilayer mirrors, replicated from plano dies.