PREPARATION OF RUGGED OPTICAL COATINGS

OPTICAL COATINGS MADE BY THERMAL OR ELECTRON BEAM EVAPORATION HAVE AN INHERENTLY IMPERFECT MICROSTRUCTURE, MAKING THEM SUBJECT TO MECHANICAL AND CHEMICAL EROSION, AND EARLY AGEING. RESEARCHERS HAVE EMPHASIZED IMPROVEMENT OF THIN FILM OPTICAL COATINGS BY TRYING TO ALTER THEIR MICROSTRUCTURE WITH VARIOUS ION-ASSISTED DEPOSITION PROCESSES. ONE PROCESS PROMISING IMPROVEMENT IS ION PLATING DEPOSITION. IN CONTRAST TO MOST OF THE ION ASSISTED DEPOSITION PROCESSES, THE PROPOSED ION PLATING TECHNIQUE EMPLOYS A LOW VOLTAGE, HIGH CURRENT PLASMA ARC BURNING INTO THE EVAPORATION SOURCE - A MODIFIED ELECTRON BEAM GUN. THEREFORE, THESE HIGH DEPOSITION RATES LEND USE TO LARGE SCALE COATINGS OF EITHER LARGE OPTICS(MIRRORS) OR OF LARGE BATCHES OF SMALL OPTICS. ION PLATED OXIDE FILMS SHOW BULK-LIKE REFRACTIVE INDICES WITH LONG-TERM STABILITY OF OVER 5 YEARS, AND NO SPECTRAL SHIFTS WITH HUMIDITY OR TEMPERATURE CYCLING. THESE IMPROVED PROPERTIES CAN BE EXPLAINED IN PART BY THE ELECTRON MICROSCOPIC OBSERVATION OF A MUCH DENSER, BULK-LIKE MICROSTRUCTURE, AS OPPOSED TO THE TYPICAL COLUMNAR MICROSTRUCTURE OF CONVENTIONAL COATINGS. THIS PROPOSAL WILL INVESTIGATE THE APPLICATION OF THESE MORE RUGGED COATINGS TO MULTI-ELEMENT OPTICAL SYSTEMS, BOTH FOR ASTRONOMICAL AND DOD APPLICATIONS.