Optical glass for prism, process for the production thereof, and optical part for prism

Abstract

An optical glass for a prism, which has high transmittance, high homogeneity and excellent thermal stability, and an optical part for a prism, which is formed of the optical glass, the optical glass being an optical glass (1) wherein the absolute value of KΔt represented by the relational expression (I), 1 K ⁢ ⁢ Δ ⁢ ⁢ t = [ ( specific ⁢ ⁢ heat × specific ⁢ ⁢ gravity ) / thermal ⁢ ⁢ conductivity ] × Young ' ⁢ s ⁢ ⁢ modulus × thermal ⁢ ⁢ expansion ⁢ ⁢ coefficient × ( 1 - Poisson ' ⁢ s ⁢ ⁢ ratio ) × photoelastic ⁢ ⁢ constant ( I ) is less than 3,000×10−2 m·s/(g·K), and (1) which contains SiO2 and B2O3 as essential components and substantially contains none of PbO and P2O5, (2) which comprises, by mol %, 60 to 85% of SiO2, 5 to 20% of B2O3, 0 to 3% of Al2O3, 0 to 3% of Li2O, 5 to 20% of Na2O, 0 to 5% of K2O, the total content of Li2O+Na2O+K2O being 6 to 20%, 0 to 5% of MgO, 0 to 10% of CaO, 0 to 10% of SrO, 0 to 10% of BaO and 0 to 10% of ZnO, the total content of MgO+CaO+SrO+BaO+ZnO being 0.1 to 15%, and substantially contains no PbO, or (3) which has a photoelastic constant of at least 2.9×10−12/Pa, and the optical part being a glass block formed of the above optical glass.

Dependencies are inferred from the claim text.