Fabrication of large circular diffractive optics

Equipment and techniques were developed at the University of Arizona for fabricating large computer-generated holograms (CGH’s) for measuring aspheric telescope mirrors. A large laser writing machine was built to fabricate binary zone plates onto spherical surfaces up to 1.8 meters in diameter and with focal ratios as fast as f/1. This machine writes 6-µm to 150-µm features with radial position accuracy better than 1 µm rms over the full diameter. The problems of applying and processing photoresist are avoided by writing the patterns using a simple thermochemical technique. Numerous holograms up to 1.2 m across have been successfully written and tested.