| 摘要 |
PROBLEM TO BE SOLVED: To provide an IR antireflection film having excellent antireflection performance to light of a IR region and excellent moisture resistance. SOLUTION: This IR antireflection film is formed by using a material of a first region having 1.2<=n1<2.0 in refractive index n1 to λ0 in the case the central wavelength of a wavelength region to be used is defined as a design main wavelength λ0 and λ0 is 2 μm<λ0<15 μm, a material of a second region having 2.0<=n1<3.0 and a material of a third region having 3.0<=n1<5.0. The first layer counted from a substrate is formed of the material of the third region and the material of the first region and the material of the third region are alternately laminated. The material of the first region is further superposed on the last layer of the material of the first region and thereafter the material of the second region is laminated as the outermost layer thereon. In such a case, Y2O3 (ittrium oxide) is used for at least one of the layers forming an even number. |
