US Patent 8693099 Antireflection film

An antireflection film capable of reliably preventing light (or laser light), which is incident on a glass substrate and which reaches a metal film, from being reflected by the metal film. The antireflection film provided between a metal film having a complex refractive index represented by NM=nM−i·km and a glass substrate having a refractive index NG includes, from the metal film side: (A) a first dielectric layer having a refractive index N1; (B) a second dielectric layer provided on the first dielectric layer and having a refractive index N2; and (C) a third dielectric layer provided on the second dielectric layer and having a refractive index N3, in which N1<nM, N1>NG, N2<NG, and N3>NG hold. Accordingly, light which is incident on the glass substrate and which reaches the metal film is prevented from being reflected by the metal film.