Patent ID: 7784307

Claim:
A process for producing an optical member made of synthetic quartz glass to be used in an optical device employing an ArF excimer laser beam or a KrF excimer laser beam as a light source at a prescribed energy density, which comprises setting the OH group concentration of the optical member depending upon the energy density of the laser beam employed, to adjust the ratio R (KJ/cm 2 ·ppb) −1 of the change in the refractive index of the optical member to the cumulative irradiation energy (KJ/cm 2 ) by the laser, to be 0≦R≦0.2, wherein the synthetic quartz glass having the set OH group concentration is obtained from a porous quartz glass body which has been simultaneously subjected to OH group-reducing treatment and transparent vitrification treatment under a reduced pressure while maintaining the temperature at a level of from 1,200 to 1,350° C. for at least 20 hours to reduce OH groups and then raised to 1,350 to 1,500° C. to carry out transparent vitrification, and wherein the OH group concentration is adjusted by the treating time and the treating temperature to a level of from 10 to 60 ppm, and then the synthetic quartz glass is held in a hydrogen atmosphere at a temperature of at most 600° C. to obtain a hydrogen-doped optical synthetic quartz glass.