Optical glass, glass material for press molding, optical element, and method of manufacturing same

摘要

Disclosed is an optical glass comprising, expressed as weight percentages, greater than or equal to 18 percent and less than 30 percent of SiO₂, greater than or equal to 12 percent and less than 23 percent of BaO, 22 to 37 percent TiO₂, greater than or equal to 7 percent and less than 16 percent Nb₂O₅, 5 to 20 percent of Na₂O, 0 to 6 percent of K₂O, 0 to 5 percent of CaO, 0 to 5 percent of SrO, 0 to 4 percent of ZrO₂, 0 to 3 percent of Ta₂O₅, 0 to 1 percent of Sb₂O₅, and greater than or equal to 0 percent and less than 0.5 percent of P₂O₅, and by essentially not comprising PbO, As₂O₃, and F. The optical glass exhibits a refractive index (nd) greater than or equal to 1.80 and an Abbé number (vd) less than or equal to 30. A method of manufacturing a glass material for press molding is disclosed. This method comprises the steps of melting the glass starting materials, forming the glass melt obtained, and annealing the formed glass and is characterized in that: the 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 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; and an annealing of said formed glass is conducted at a temperature lower than the glass transition temperature.