Patent ID: 7196027

Claim:
An optical glass consisting of, in mass %, SiO 2 40–70% PbO 14–50% Na 2 O and/or K 2 O in the total amount of 8–17% where Na 2 O 6.5–14% and K 2 O 0–15% B 2 O 3 0–1.7% Sb 2 O 3 0–1% Al 2 O 3 0–0.4% BaO 0–5% and a total amount of 0.1–2% of F in one or more fluoride or fluorides as the fluorine ingredient substituting for the above oxide or oxides partially or entirely and/or 0.001–0.2% of TiO 2 and/or 0.001–1% As 2 O 3 , and an amount of change in refractive index (Δn:difference in refractive index between a state before radiation and a state after radiation) caused by radiation of a laser beam at a wavelength of 351 mm with an average output power of 0.43 W, pulse repetition rate of 5 kHz and a pulse width of 400 ns for one hour of 5 ppm or below.