SYNTHETIC SILICA GLASS WITH UNIFORM FICTIVE TEMPERATURE

摘要

PROBLEM TO BE SOLVED: To provide a method for making silica glass with a uniform fictive temperature which makes glass in which variation in a refractive index and birefringence is reduced.;SOLUTION: The silica glass has a strain point T_s, a fictive temperature and a relaxation rate at the fictive temperature, and also has hydroxy group concentration of less than 800 mass ppm. The hydroxy group concentration varies only at least by 0.5 ppm. The silica glass is heated at a target fictive temperature, or heated or cooled at a rate that is less than the rate of change of the fictive temperature, for a time that is sufficient to allow the fictive temperature of the glass to come within 3°C of the target fictive temperature. The silica glass is then cooled from the target fictive temperature to a temperature below the strain point of the glass at a cooling rate that is greater than the relaxation rate of the glass at the target fictive temperature. The silica glass has a fictive temperature that varies by less than 3°C after the annealing step.;COPYRIGHT: (C)2011,JPO&INPIT