Analysis of mid-spatial frequency errors in two dimensions at metal mirror fabrication

The wish for smaller and lighter telescopes, better image quality, and shorter wavelength applications sets ever increasing demands towards the quality of optical surfaces. In metal mirror fabrication with diamond turning, mid spatial frequency errors become the most limiting factor in achieving a certain surface quality, and reducing them puts high requirements on the manufacturing. A first step in improving the surface quality is to utilize appropriate analysis methods that account for the highly anisotropic surfaces developing at diamond turning. In this article, a novel, two-dimensional representation of the power spectral density is demonstrated, which takes up the many benefits of the established PSD and extends it to meet the demands of anisotropic surfaces.