Polishing PMMA and Other Optical Polymers with Magnetorheological Finishing

LLE Review, Volume 96 239 Introduction Polymer optics are typically manufactured by injection molding (thermoplastics, high volume, economical), compression molding (thermosets, higher precision, and larger sizes), or diamond turning. Once formed by these techniques, polymer components are used “as manufactured,” usually without further cold working to improve surface finish or figure. This is because optical polymers are soft and possess high linear expansion coefficients and poor thermal conductivities.1 Attempts to improve surface finish and figure using conventional grinding and polishing processes usually result in scratching, the embedding of abrasive particles, the formation of “orange peel,”2 and degradation to surface figure. There are circumstances when it would be desirable to perform a classical polishing operation on a polymer surface. In some instances it is desirable to drive rms surface roughness values below 2 to 4 nm in preparation for deposition of a coating. In other applications, reduced surface form errors are required. It is advantageous to eliminate the unwanted flare from diamondturning marks on polymer optics in order to test prototype imaging system designs.