WIDE-BAND REFLECTION PREVENTIVE FILM WITH FOUR SPUTTERED LAYERS

摘要

PROBLEM TO BE SOLVED: To economically obtain the reflection preventive film by serial magnetron sputtering by incorporating a 3rd layer which has a specific refractive index and specific optical thickness. SOLUTION: A 1st layer 26 on the top surface 24 of a substrate 22 has an intermediate or high refractive index which is larger than about 1.9 and preferably has optical thickness which is <=1/4 as large as the center wavelength of the reflection preventive film. A 2nd layer 28 has a refractive index which is less than about 1.5 and preferably has optical thickness which is <=1/4 as large as the center wavelength. The optical thickness of the 3rd layer 30 may be <=1/6, 1/7, or 1/8 as large as the center wavelength. A 4th layer 32 has a low refractive index and preferably has optical thickness which is about 1/4 as large as or a little larger than the center wavelength. The low-refractive- index materials of the layers 28 and 32 are silicon dioxides having <=20% other materials. The high refractive index material of the layer 30 is TiO2 .