| 摘要 |
PROBLEM TO BE SOLVED: To improve the optical performance of the light passed through an optical unit by absorbing unnecessary diffracted light in the optical unit. SOLUTION: The beam of light 23 which is made incident on a diffraction optical element 22 is diffracted as a desired primary light and an unnecessary light ray 25 is also diffracted. A luminous flux absorbing structure 26, consisting of horn-shaped recessed parts 28 and 29, where inside surface is used as a reflection surface, are provided on the extended line in progressing direction of the unnecessary light 26. Therefore, the unnecessary light ray 25 can be absorbed by reflecting in the recessed parts 28 and 29. Also, by providing cooling means 30a and 30b in close vicinity of the luminous flux absorbing structure 26, the luminous flux absorbing structure, which is heated up by the light ray 25, can be cooled down.
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