| 摘要 |
PROBLEM TO BE SOLVED: To obtain an anti-reflection film which has a very effective and excellent anti-reflection characteristic to two wavelength ranges such as ultraviolet rays of 200 nm or smaller wavelengths and visible light between 600 nm and 700 nm wavelengths and to obtain an optical system provided with it. SOLUTION: An anti-reflection film consisting of four thin films of a 1st layer, a 2nd layer, a 3rd layer and 4th layer provided on a transparent substrate sequentially from the substrate side to the air side, the 1st and 3rd layers are composed of LaF3 or its mixture and the 2nd and 4th layers are composed of MgF2 or its mixture. Then, when the refractive index of this MgF2 or its mixture is expressed by nm and that of the LaF3 or its mixture is expressed by nl, the refractive indices to light of a 193 nm wavelength are made so as to satisfy the relations of 1.60<=nl<=1.80 and 1.32<=nm<=1.52. |
