Investigation of the two-dimensional power spectral density (2-D-PSD) and rms-roughness Sq on polished optical surfaces

Current standardisation of defects and quality of optical surfaces as ISO 10110 are mainly based on one-dimensional scanning methods. However, new instruments as confocal microscopes, white-light interferometers or atomic force microscopes (AFM) provide the possibility to generate three-dimensional surface profiles. Out of the three-dimensional surface data it is possible to calculate two-dimensional power spectral density. In theory the 2-D-PSD directly allows conclusions to be drawn about the surface properties like anisotropic textures or polish quality. Within the scope of this presentation ten optical glass surfaces are investigated with an AFM. The gained data are analysed on the surface parameters rms-roughness Sq and 2 D-PSD. In comparison with previous Sq-values measured by white-light interferometer the Sq-values measured by AFM show clear deviations. Different 2-D-PSD-graphs are shown on the poster and the connection to surface topographies are visualised by AFM pictures. Due to the 2-D-PSD data the mentioned connections between the graphs and anisotropic textures and polishing quality are shown.