Diamond machining of aspherical and freeform mirrors

The fabrication of metal mirrors with aspherical surface or freeform is increasingly discussed by optical community. The technical advancements allow a high accuracy in freeform manufacturing. Another enabler is the implementation of freeform elements into modern optical design tools. Diamond machining like turning or milling are ultra-precise techniques especially for the fabrication of metal mirrors. With the development of diamond machines in the early 1970s diamond turning became an accepted manufacturing approach for the fabrication of rotational symmetrical optics, such as flats, spheres and aspheres for IR-applications. Applications in the VIS or UV spectral range require outstanding form and roughness. Therefore, post-polishing and post-figuring processes are applied on amorphous coatings on thermally matched mirror substrates. Modern servo-assisted techniques allow the fabrication of off-axis mirrors in the center of the turning axis. The expected benefits are reduction of the surface shape deviation coming from centrifugal force and the chance to correct non-rotationally symmetric errors. Referring to this, the manufacturing of reference marks and interfaces are mandatory for measurement and integration. A hybrid fabrication process comprising a diamond freeform turning and a diamond milling in one and the same ultra-precision setup for manufacturing of freeform will be presented.