| 摘要 |
Where n is the refractive index of the thin film 2 , and d is the thickness of this thin film 2 , respective substances may be considered to be formed on the surface of the substrate 1 with a thickness of d by a substance having a refractive index of n in the areas where the thin film 2 is left completely intact, with a thickness of d by a substance having a refractive index of 1 in the areas where the thin film 2 is completely removed, and with a thickness of d by a substance having a effective refractive index determined by the diameter of the cylinder and the thickness d of the thin film 2 in other areas. In actuality, the diffraction type diffusion element is divided not into 9 regions, but rather into numerous regions, with each part having a structure such as that shown in the figure, and with the effective refractive indices of the respective parts being different. Furthermore, a diffusion element which has the desired characteristics can be formed by varying the ratio of these different effective refractive indices.
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