Aspheric Surface Generation Requirements for Magnetorheological Finishing

A manufacturing system for grinding and polishing aspheres is under development at the Center for Optics Manufacturing (COM). Polishing is accomplished using the magnetorheological finishing (MRF) technique. MRF utilizes the unique properties of MR fluids to achieve high polishing removal rates. The fluid is carried through a magnetic field, in which its viscosity is increased by several orders of magnitude. The lens is polished in this viscous zone to optical quality. MRF is very effective at polishing high spatial frequency errors (microroughness) and at figuring global form errors (e.g. power), but has limitations for smoothing of mid-frequency errors. The work presented here will describe the problematic mid-spatial frequency regime, and use this a criteria for the aspheric grinding process.