PRODUCTION OF TITANIUM-FREE SAPPHIRE FOR CESIUM CELL APPLICATIONS

THE CESIUM RESONANCE FILTER IS AN IMPORTANT ELEMENT FOR THE BLUE-GREEN LASER REQUIRED BY THE NAVY FOR UNDERWATER COMMUNICATION. DURING FABRICATION OF PROTOTYPES OF THIS FILTER IT WAS OBSERVED THAT THE SAPPHIRE ELEMENTS PRODUCED PULSE SIGNALS WHICH COULD NOT BE ELIMINATED. IT IS NOW KNOWN THAT TITANIUM (TI) IMPURITIES IN SAPPHIRE PRODUCED THESE PARASITIC PULSE SIGNALS IN CESIUM CELL CONFIGURATION. THE SOURCE OF TI IMPURITIES IS THE MELTSTOCK UTILIZED FOR SAPPHIRE CRYSTAL GROWTH. THE PROPOSED PROGRAM IS TO GROW 4-INCH DIAMETER SAPPHIRE CRYSTALS UTILIZING THE HEAT EXCHANGER METHOD (HEM) WITH THE EMPHASIS OF MINIMIZING TI CONTAMINATION BY SELECTION OF MELTSTOCK AND DEVELOPING CRYSTAL GROWTH PARAMETERS. IT IS ALSO INTENDED TO UTILIZE HIGH-PURITY ALUMINA POWDERS INSTEAD OF THE CONVENTIONAL SAPPHIRE CRACKLE AS MELTSTOCK FOR CRYSTAL GROWTH. SAMPLES WILL BE CHARACTERIZED FOR FLUORESCENCE FOR TI AND FOR PRESENCE OF PULSE SIGNALS IN CESIUM CELL APPLICATIONS. ONCE THE FEASIBILITY OF PRODUCING "TITANIUM-FREE" SAPPHIRE IS ESTABLISHED THESE PROCEDURES WILL BE ADOPTED FOR GROWTH OF LARGER SAPPHIRE BOULES BY HEM DURING THE PHASE II PROGRAM.