Control of nano-topography on an axisymmetric ground surface

The use of aspherical optical parts has become common as optical instruments are becoming smaller with and are achieving higher resolution. Nano-order roughness and high-precision shapes are simultaneously required for the surface of aspherical optical parts. At present, form accuracy of the aspherical lens becomes less than 50 nm, and the maximum height roughness becomes less than 20 nm. These values of form accuracy and maximum height roughness satisfy the requirement for most precision optical parts. However, nano-topography, which causes grinding marks and deteriorates accuracy of optical parts, is generated on the ground surface. Conventional evaluation criteria such as form accuracy and surface roughness cannot estimate the nano-topography. In the present paper, the cross sectional profile of the axisymmetric ground surface is calculated in order to estimate the distribution of the nano-topography. As a result, the possibility of control of the nano-topography distribution is confirmed. In addition, controlling the amplitude of nano-topography is easier than controlling the distribution of nano-topography.