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

Abstract

Disclosed is an optical glass comprising, expressed as weight percentages, greater than or equal to 18 percent and less than 30 percent of SiO, greater than or equal to 12 percent and less than 23 percent of BaO, 22 to 37 percent TiO, greater than or equal to 7 percent and less than 16 percent NbO, 5 to 20 percent of NaO, 0 to 6 percent of KO, 0 to 5 percent of CaO, 0 to 5 percent of SrO, 0 to 4 percent of ZrO, 0 to 3 percent of TaO, 0 to 1 percent of SbO, and greater than or equal to 0 percent and less than 0.5 percent of PO, and by essentially not comprising PbO, AsO, 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 cmat wavelengths of from 400 to 2,500 nm or comprises crystals with a volumetric ratio of less than 10, 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 10to 10dPa·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 cmor comprises crystals with a volumetric ratio of greater than 10; and an annealing of said formed glass is conducted at a temperature lower than the glass transition temperature.