Freeform Optical Systems for Defense System Optics

Freeform optical surfaces offer advantages over axisymmetric surfaces in the ability to reduce optical sizes, increase performance and reduce aberrations. However, the description, fabrication and metrology of these surfaces can be difficult and costly, prohibiting their ability to achieve their full potential. Fabrication of these surfaces can be difficult since they are not axisymmetric and have varying local radii of curvature, rendering grinding, lapping and polishing of these surfaces untenable. A method to overcome the difficulties in fabrication of freeform surfaces is to apply ductile mode machining (DMM) to eliminate grinding, lapping and polishing. DMM has been demonstrated on SiC mirror representative of freeform optics in Phase I. Through the use of physics-based modeling, DMM conditions can be identified where material removal results in ductile chip formation, damage free surfaces and excellent surface finish. This STTR activity extends the technology of DMM to freeform configurations enabled by physics-based modeling techniques. We will further develop, enhance and validate the modeling capability and apply it to CVD coated SiC freeform optics. Backed by modeling data, we will perform a set of machining experiments to ascertain the DMM operating envelope and subsequently demonstrate the fabrication of a full scale freeform optic.