| 摘要 |
PROBLEM TO BE SOLVED: To provide an antireflection film having a high reflectance in both of the UV region and the visible region. SOLUTION: The antireflection film is applied onto a substrate consisting of quartz or fluorite. The first, third, fifth and seventh layers from the substrate side are formed of an HfO2 film, and the second, fourth and sixth layers are formed of an SiO2 or an MgF2 film, and the eighth layer is formed of a MgF2 film. It is characterized in that the optical film thickness nd of each layer ranges, with respect to the reference wavelength λ, (0.15 to 0.25)×λ/4 for the first layer, (0.39 to 0.52)×λ/4 for the second layer, (0.31 to 0.41)×λ/4 for the third layer, (0.21 to 0.34)×λ/4 for the fourth layer, (2.3 to 3.0)×λ/4for the fifth layer, (0.27 to 0.43)×λ/4 for the sixth layer, (0.20 to 0.27)×λ/4 for the seventh layer, and (1.0 to 1.2)×λ/4 for the eighth layer. |
