Optical glass for precision press molding and optical element

Abstract

An optical glass for precision press molding that has desired optical constants, a low glass transformation point (Tg), and a devitrification temperature that is lower than a temperature of a glass melt, at which a viscosity suitable for forming of a preform material is obtained, is provided. The optical glass for precision press molding has a lanthanum borosilicate system glass having optical constants of refractive index (nd) within a range from 1.65 to 1.73 and Abbe number (νd) within a range from 50 to 60, a Tg within a range of 480-580° C. The optical glass for precision press molding has a devitrification temperature that is lower than a temperature of the glass melt when the glass melt has a viscosity η (poise) of log η=2.5. The optical glass for precision press molding has a specific composition range of SiO2—B2O3—La2O3—Y2O3—Ta2O5—CaO—Li2O system composition.

Dependencies are inferred from the claim text.