Recent Advances in the Application of Computer Controlled Optical Finishing to Produce Very High Quality, Transmissive Optical Elements and Windows

摘要

Large aperture (20-inch diameter) sapphire optical windows have been identified as a key element of new and/or upgraded airborne electro-optical systems. These windows typically require a transmitted wave front error of much less than 0.1 waves rms @ 0.63 microns over 7 inch diameter subapertures. Large aperture (12.36-inch diameter by 5.1-inch thick) sapphire substrates have also been identified as a key optical element of the Laser interferometer Gravitational Wave Observatory (LIGO). This project is under joint development by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology unAer cooperative agreement with the National National Science foundation (NSF). These substrates are required to have a transmitted wave front error of 10 nm (0.016 waves) rms @ 0.63 microns over a 200 mm (7.9-inch) subaperture. Owing to the spatial variations in the optical index of refraction potentially anticipated within 20-inch diameter sapphire, thin (0.25 - 0.5-inch) window substrates, as well as within the 12.36-inch diameter by 5.1-inch thick substrates for the LIGO application; our experience tells us that the required transmitted wave front errors can not be achieved with standard optical finishing techniques as they can not readily compensate for errors introduced by inherent material characteristics. Computer controlled optical finishing has been identified as a key technology likely required to enable achievement of the required transmitted wave front errors. Goodrich has developed this technology and has previously applied it to finish high quality sapphire optical windows with a range of aperture sizes from 4-inch to 13-inch to transmitted wavefront errors satisfying these new requirements. This paper addresses the successful recent developments and accomplishments in the application of this optical finishing technology to sequentially larger aperture and thicker sapphire windows to achieve challenging transmitted wave front error requirements defined above.