US Patent 7563736 Optical glass and process for producing optical element

An optical glass which has an internal transmittance to a light having a wavelength of 400 nm being at least 90% as calculated in a thickness of 1 mm and which contains at least 25 mol % of B2O3 and from 0.1 to 20 mol % of TeO2. The above optical glass which contains La2O3. The above optical glass wherein the glass transition point ≦650° C. and the refractive index at 633 nm≧1.70. A process for producing an optical element made of the above optical glass, which comprises dropping the optical glass in a molten state from a flow outlet of a flow out pipe made of a platinum alloy to form a preform and subjecting it to precision press-molding.