Advancements in Non-Contact Freeform Metrology with Datum Structures

Freeform optical components are becoming more prevalent in the precision optics industry. Metrology of freeform surfaces is traditionally limited to coordinate measuring machines, or computer-generated holograms. OptiPro has developed UltraSurf, a non-contact metrology platform that has been adapted to measuring freeform surfaces. The non-contact probing method, and multiple axes of motion allow UltraSurf to scan freeform optical surfaces and the associated datum structures. Datum structures define a coordinate system that all the freeform surfaces of a component can be referenced for metrology and manufacturing. Iterative corrective grinding and polishing is dependent on accurately locating the form error map to the surface within the machine. Measuring the datums along with the surface provides an absolute reference for the form error map. Allowing an operator to correct form error with confidence that the machine will grind or polish in the correct location. Datum and optical surface metrology together will allow referencing multiple freeform surfaces to each other, which is critical on transmissive freeform systems. Practical examples of non-contact freeform metrology with the UltraSurf will be presented along with considerations of datum features.