Freeform Optical Systems for Defense System Optics

Freeform optical surfaces offer advantages over axis-symmetric 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 axis-symmetric and have varying local radii of curvature, rendering grinding, lapping and polishing of these surfaces to be onerous operations. 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 successfully applied to SiC mirror surfaces to achieve the requisite surface finish and figure error for axis-symmetric optics. 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 and enhance its modeling capability and apply to CVD coated SiC freeform optics. In Phase I we will demonstrate the feasibility of DMM to machine a freeform surface in a laboratory environment.