Patent ID: 7189460

Claim:
A high reflectance mirror comprising a substrate and a silver film, a low refractive index film and a high refractive index film formed on the substrate in this order wherein an adhesion improving film is formed on the silver film surface on the opposite side of the substrate, the extinction coefficient of the low refractive index film is at most 0.01, the extinction coefficient of the high refractive index film is at most 0.01, the adhesion improving film is an oxide film and the extinction coefficient of the adhesion improving film is at most 0.1; wherein the geometric film thickness of the silver film is from 60 to 200 nm, the geometric film thickness of the low refractive index film is from 25 to 60 nm, the geometric film thickness of the high refractive index film is from 30 to 65 nm and the geometric film thickness of the adhesion improving film is from 3 to 14 nm; wherein the silver film is an alloy film of silver and gold; wherein an undercoat film is formed on the silver film surface on the side of the substrate, the geometric film thickness of the undercoat film is from 1 to 20 nm, and the material of the undercoat film is at least one selected from the group consisting of zinc oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, niobium oxide and chromium oxide; wherein the material of the adhesion improving film is at least one selected from the group consisting of zinc oxide, tin oxide, indium oxide and aluminum oxide; and wherein the material of the low refractive index film is silicon oxide; wherein the material of the high refractive index film is at least one selected from the group consisting of niobium oxide, zirconium oxide, tantalum oxide, hafnium oxide, titanium oxide and tin oxide.