Patent ID: 8334938

Claim:
A laminated thin film, comprising: a substrate; and at least two types of materials laminated on the substrate, the laminated thin film has a transmittance of 95% or higher in a working wavelength band with respect to both P-polarized light and S-polarized light, and the following expression (1) is satisfied with respect to a light ray of a specific wavelength λ 0 contained in the working wavelength band, and the following expressions (2) and (3) are always satisfied in a range of 0<θ≦15 degrees, 0.25 < ( n H · d H + n L · d L ) / λ 0 < 0.5 ( 1 ) 0.95 ≤ Δ ⁡ ( θ ) A ⁢ ⁢ sin 2 ⁢ θ ≤ 1.05 ( 2 ) where , A = Δ ⁡ ( 10 ⁢ ° ) sin 2 ⁡ ( 10 ⁢ ° ) ,  Δ ⁡ ( 10 ⁢ ° )  ≥ 2.0 ⁢ ( degrees ) ( 3 ) where an average film thickness of a material having relatively high refractive index n H is represented by d H , an average film thickness of a material having relatively low refractive index n L is represented by d L of the materials forming the laminated thin film, and a phase difference received by a light ray entering at an angle θ with respect to a normal of a surface of the laminated thin film is represented by Δ(θ).