| 摘要 |
PROBLEM TO BE SOLVED: To provide a quartz glass preform having a uniform refractive index and made into transparent glass by substantially uniformly adding fluorine in a holding furnace to a porous quartz obtained by a vapor phase method. SOLUTION: This quartz glass preform having a high uniform refractive index but not higher than 10×10<SP>-6</SP>is obtained by sintering and making into a transparent glass a porous quartz, which is prepared by heating, before fluorine treatment, a porous quartz 3 in an inactive gas atmosphere at a temperature of 800-1,200°C for not shorter than 5 hours in a holding furnace 1 and making the difference between its surface temperature and the temperature at the center within 30°C, then, heating the porous quartz 3, in the same way, at a temperature of 800-1,200°C for not shorter than 5 hours in a fluorine compound gas atmosphere, and adding the fluorine uniformly in the porous quartz 3. COPYRIGHT: (C)2004,JPO&NCIPI
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