| 摘要 |
PURPOSE:To prevent occurrence of dispersion due to the state of the surface of a substrate having a concave surface, by forming the first layer of dielectric multilayer film with a protecting film against abrasives for the concave surface part when the flat part of the substrate having the concave surface is formed. CONSTITUTION:A substrate 11 is formed with glass having low thermal expansion coefficient. The surface, on which a dielectric multilayer film 10 is formed, is formed as a concave surface having a specified radius of curvature. On a concave surface 14 of the substrate 11, the multilayer film 10 is laminated. The first layer of the multilayer film 10 on the side of the substrate 11 becomes a protecting film 16. The protecting film 16 comprises a material, which can protect the surface from abrasives, e.g., the material comprises tantalum pentoxide or aluminum oxide. Thus the occurrence of dispersion due to the state of the surface of the substrate is prevented. |
