POLISHING OF SAPPHIRE FOR OPTICAL APPLICATIONS

CURRENT PROCESSES FOR MANUFACTURING SAPPHIRE INTRODUCE A NUMBER OF DEFECTS SUCH AS DIE MARKS AND GROWTH ARTIFACTS IN THE AS-GROWN SAPPHIRE BLANK. THUS, THESE MATERIALS NEED TO BE POLISHED PRIOR TO USE IN OPTICS. THE OBJECTIVE OF THIS PROJECT IS TO DEVELOP A HIGH-QUALITY, HIGH-SPEED, COST-EFFECTIVE TECHNIQUE FOR POLISHING SAPPHIRE BASED OPTICS. THE TWO METHODS CURRENTLY USED FOR POLISHING SAPPHIRE ARE: MECHANICAL AND MECHANOCHEMICAL, BOTH OF WHICH INVOLVE SCRAPING, GRINDING AND USING ABRASIVES SUCH AS DIAMOND OR COLLOIDAL SILICA. THESE METHODS ARE EXPENSIVE BECAUSE OF THE LONG TIMES REQUIRED FOR POLISHING. FURTHER, DUE TO THE APPLICATION OF MECHANICAL PRESSURE, HEAT IS GENERATED AT THE POLISHING INTERFACE LEAVING BEHIND DEFECTS THAT AFFECT OPTICAL PERFORMANCE. THE PROOF-OF-CONCEPT IS BEING ESTABLISHED BY USING A DUAL STAGE NON-CONTACT METHOD TO REMOVE PLANAR LAYERS OF THE SAPPHIRE THUS ACHIEVING SURFACE ROUGHNESS ON THE ORDER OF ANGSTROMS IN BOTH FLAT AND CURVED BLANKS. OPTICAL CHARACTERIZATION IS PERFORMED ON THE POLISHED SAMPLES AND CORRELATED TO THE PROCESSING PARAMETERS.