Optical glass, precision press-molding preform, process for producing the preform, optical element and process for producing the element

摘要

An optical glass having high refractivity and a low sag temperature and having a low-temperature softening property that enables precision press-molding is provided, and the optical glass contains, by mol %, 5 to 50% of B₂O₃, 3 to 50% of SiO₂, 5 to 40% of TiO₂, 1 to 40% of ZnO, 5 to 20% of La₂O₃, 0 to 10% of Gd₂O₃, 0 to 15% of Nb₂O₅, 0 to 10% of ZrO₂, 0 to 5% of Ta₂O₅, 0 to 10% of Bi₂O₃, 0 to 10% of MgO, 0 to 8% of CaO, 0 to 10% of SrO, 0 to 10% of BaO, provided that the total content of MgO, CaO, SrO and BaO is 15% or less, 0 to 20% of Li₂O, and 0 to 5% of Na₂O, optionally containing Sb₂O₃ as a refining agent, and having a refractive index (nd) of 1.8 or more and an Abbe's number (vd) of 35 or less.