Abstract: A measuring apparatus has at least two radiation sources arranged to illuminate a measuring region of a surface of a sample, the at least two sources configured to illuminate the measuring region along at least two illumination beam paths at different angles of incidence relative to a surface normal of the surface, a detector device configured to detect at least two scattered radiation images of surface sections in the illuminated measuring region at a predetermined viewing angle relative to the surface normal of the surface, portions of the scattered radiation received by the detector device, which portions are formed in each case by the illumination in one of the illumination beam paths, in each case having a common spatial frequency, and an evaluation device configured to determine at least one roughness feature of the surface sections from the at least two scattered radiation images.

Abstract: A Fresnel rhomb which can be used over a wide range of wavelengths, including wavelengths below 250 nm, takes into account the orientation of the crystal structure of the rhomb during manufacturing of the rhomb and adjusts the entrance side of the front end in relation to the direction-dependent birefringence. The beam incident on the Fresnel rhomb always forms a set angle of 90° with the front end in order to achieve the desired effect. If the orientation of the crystal structure is taken into account when the front end is manufactured and appropriately adjusted, the light beam will follow a given direction through the crystal. In such a way non-isotrop properties of the material can be considered and used for the desired application. One of such non-isotrop properties of the material is, for example, the direction-dependent birefringence when using CaF2, BaF2 or similar materials.