Patent ID: 8479539

Claim:
A method of manufacturing optical elements comprising: (A) preparing a glass material for press molding by (a) melting glass starting materials, including SiO 2 , TiO 2 , and Nb 2 O 5 to obtain a glass melt, (b) forming the glass melt obtained in the melting step into a formed glass, and (c) annealing the formed glass to obtain a glass material for press molding; (B) press molding the glass material by reheating the glass material in a mold to soften the glass material and applying pressure to the glass material to make a glass blank; and (C) grinding and polishing the glass blank to obtain an optical element, wherein said glass melt has a composition such that, (1) when rapidly cooled to room temperature, said glass melt becomes glass that has a scattering coefficient of less than 0.005 cm −1 at wavelengths of from 400 to 2,500 nm or comprises crystals with a volumetric ratio of less than 10 −6 , and (2) when maintained for three hours at a temperature 10° C. higher than the glass transition temperature, maintained for 10 min at a temperature yielding a viscosity of 10 4.5 to 10 3.5 dPa·s, and then rapidly cooled to room temperature, said glass melt becomes glass that has a scattering coefficient at least one wavelength from 400 to 2,500 nm of greater than 0.01 cm −1 or comprises crystals with a volumetric ratio of greater than 10 −5 ; wherein said glass material for press molding is comprised of glass that (i) has a scattering coefficient of greater than or equal to 0.01 cm −1 at least one wavelength of from 400 to 2,500 nm or comprises crystals with a volumetric ratio of greater than 10 −5 , when maintained for three hours at a temperature ten degrees higher than the glass transition temperature, maintained for ten minutes at a temperature at which it exhibits a viscosity of 10 4.5 to 10 3.5 dPa·s, and rapidly cooled to room temperature, (ii) has a scattering coefficient of glass interior at least one wavelength from 400 to 2,500 nm of less than 0.005 cm −1 or comprises in interior crystals with a volumetric ratio of less than 10 −6 , when maintained for 10 min at a temperature yielding a viscosity of 10 4.5 to 10 3.5 dPa·s and then rapidly cooled to room temperature, and (iii) has a weight ratio of Nb 2 O 5 /TiO 2 that is within a range of equal to or greater than 0.189 to equal to or less than 0.56, wherein said annealing of said formed glass is conducted at a temperature lower than the glass transition temperature, and wherein the combined content of TiO 2 and Nb 2 O 5 of said glass material is greater than or equal to 35 weight percent.