| 摘要 |
PROBLEM TO BE SOLVED: To provide an antireflection film and an optical element with low reflectance with respect to wavelength regions in the vicinity of 365 nm or 436 nm and with broad band, effective and excellent antireflection characteristics. SOLUTION: The antireflection film is a multilayer film with four-layered structure formed on a substrate. A first layer and a third layer numbered successively from the substrate side are high refractive index layers with 2.10-2.40 refractive index in 320-450 nm wavelength range. A second layer and a fourth layer are low refractive index layers with 1.42-1.50 refractive index in the same range. Denoting optical film thickness of the first layer to the fourth layer as d1-d4 respectively and the wavelength in use in the same wavelength range as λ0, inequalities 0.05λ0<=d1<=0.07λ0, 0.05λ0<=d2<=0.11λ0, 0.50λ0<=d3<=0.56λ0 and 0.24λ0<=d4<=0.26λ0 hold. The antireflection film optionally has the construction with an exchange of the second layer for a medium refractive index layer. The optical element consists of the antireflection film formed on the substrate. |
