| 摘要 |
A beam splitter, comprises: a light source light entering side prism to which a light from a light source enters; a reflected light entering side prism to which a reflected light from an information recording medium enters; a multi layer film provided between the light source light entering side prism and the reflected light entering side prism, wherein the multi layer film comprises a plurality of specific laminated sections each of which comprises a low refractive index layer, a medium refractive index layer, and a high refractive index layer in this order from the reflected light entering side.
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