EFFECTS OF PROCESS GAS ENVIRONMENT ON PLATINUM-INCLUSION DENSITY AND DISSOLUTION RATE IN PHOSPHATE LASER GLASSES

The effects of process gas environment on reducing the density of plat inum inclusions in phosphate laser glasses are examined. The platinum inclusions originate from the crucibles used to melt the laser glass a nd can lead to optical damage in glasses used in high-peak-power laser s. The melting experiments examine the effects of N-2 O-2 and Cl-2 gas es on inclusion density and platinum dissolution rates. The more oxidi zing the process gas conditions, the greater the dissolution rate (O-2 + Cl-2 > O-2 much greater than N-2). A thin-film mass transport model is used to analyze dissolution rate data for small plates of platinum over a range of temperatures from 1000 to 1200 degrees C and oxygen f ugacity of 10(-3) to 1 bar. At 1200 degrees C the platinum dissolution rate is approximately 3.0.10(-8) (P-O2)(0.7)(in g/cm(2).s)) where P-O 2 is the oxygen fugacity of the process gas in bar. Using Cl-2 rather than O-2 causes a measurable increase in the optical absorption of the glass that may be due to either a red-shift and/or a greater absorpti on coefficient for the platinum-chlorine complex.