PRODUCTION OF FLUORIDE GLASS PREFORM

摘要

PURPOSE: To obtain a fluoride glass preform not causing impregnation of water, etc., from environmental atmosphere by pouring plural fluoride glass melt into a mold having prescribed constitution under specific conditions and cooling and solidifying the melt. CONSTITUTION: A mold comprises an opening hollow part 110 for pouring plural kinds of fluoride glass, a cylindrical first hollow part 120 and a cylindrical second hollow part 130 having the central axis which coincides with the first hollow part 120 and end parts larger than the first hollow part 120. A glass melt (A) 410 which has the first material composition having nearly same amount as the sum of each volume of the first hollow part 120 and second hollow part 130 from the opening hollow part 110. The glass melt (B) 420 having the second material composition is poured onto the melt A by such amount that the volume after solidifying the melt B 420 becomes smaller than a volume decreased from the melt-like state when the melt A 410 is solidified. Further, the glass melt 430 having the third material composition is poured onto the melt B 420. Then, the mold 100 is cooled in an inert gas atmosphere to solidify.