Patent ID: 7111477

Claim:
A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of preform in said range for a definite time, lowering the temperature, wherein the temperature is lowered with a temperature difference of from 1 to 20° C. between a first temperature T 1 of a light transmitting surface of the optical synthetic quartz glass preform and a second temperature T 2 of an outer peripheral side surface of the optical synthetic quartz glass preform with said temperatures lowering at rates of from 2 to 50° C./hour, wherein, in the temperature-lowering step, the first temperature T 1 is lower than the second temperature T 2 , the light transmitting surface being substantially entirely at the first temperature T 1 and the outer peripheral side surface being substantially entirely at the second temperature T 2 .