HEAT TREATMENT METHOD OF SYNTHETIC QUARTZ GLASS

摘要

A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a maximum/minimum difference (”OH) of less than 350 ppm involves the steps of first heat treatment of holding at 1,150-1,060°C for a time of 0.5-10 hours, cooling down to a second heat treatment temperature at a rate of -7°C/hr to -30°C/hr, second heat treatment of holding at 1,030-950°C for a time of 5-20 hours, and annealing at a rate of -25°C/hr to -85°C/hr. Two stages of heat treatment ensures that the glass has a low birefringence. A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a maximum/minimum difference (”OH) of at least 350 ppm involves first and second heat treatments and annealing, wherein the duration of the second heat treatment is from 10 to 15 hours