PRODUCTION OF SYNTHETIC QUARTZ GLASS PREFORM

摘要

PROBLEM TO BE SOLVED: To obtain a synthetic quartz glass material contg. impurities at a low ratio and has a uniform refractive index by executing a preliminary calcining stage under specific conditions with porous synthetic quartz glass formed by a gaseous phase axial deposition method and heating up the quartz glass and executing a clarifying stage after the execution of the calcining stage. SOLUTION: A high-purity silicon compd. which is a raw material is hydrolyzed by using an ordinary oxyhydrogen flame by the gaseous phase axial deposition method by which the porous synthetic quartz glass (soot body) is obtd. This soot body is heat treated at 1300 to 1400 deg.C for 1 to 5 hours under a pressure of 1.5 to 50 PASCAL as the preliminary calcining stage, by which the density is made homogeneous. The soot body is then heated for 10 to 40 hours at 1200 to 1300 deg.C under the same pressure to remove the moisture and is then heated up at a rate of 0.5 to 5 deg.C/minute and is subjected to the clarifying treatment for 3 to 8 hours at about 1420 to 1600 deg.C. The soot body is thereafter slowly cooled at <5 deg.C/minute from at least the temp. above 1500 deg.C. Further, the soot body is heated at 610 to 790 deg.C in a gaseous hydrogen atmosphere of 1×10<3> to 1×10<6> Pa and is doped with hydrogen, by which the laser resistance is imparted to the glass preform.