Patent ID: 8713969

Claim:
A method for adjusting the zero crossover temperature of a silica-titania glass, the method comprising the steps of: preparing a consolidated silica-titania glass boule having a titania content in the range of 5-20 wt %, annealing the consolidated silica-titania glass boule using a first anneal cycle to form a silica-titania glass having an initial state, the initial state including an initial zero crossover temperature Tzc 0 and an initial fictive temperature Tf 0 , determining the initial zero crossover temperature Tzc 0 and the initial fictive temperature Tf 0 of the silica-titania glass, specifying a target state for the silica-titania glass, the target state including a target fictive temperature Tf(TARGET) and a target zero crossover temperature Tzc(TARGET), subjecting the silica-titania glass to a second anneal cycle, the second anneal cycle transforming the silica-titania glass from the initial state to the target state, the conditions of the second anneal being determined using the function Tf (TARGET)= f ( Tf 0 ,Tzc 0 ,Tzc (TARGET)) wherein the target zero crossover temperature Tzc(Target) of the silica-titania glass is within ±10° C. of the initial crossover temperature Tzc 0 of the silica-titania glass.