| 摘要 |
A diffractive optical element includes stacked first and second diffraction gratings made of different materials. The materials of the first and second diffraction gratings are glass. The first and second diffraction gratings have grating surfaces contacted to each other. The materials satisfy a predetermined condition when Tg2 and At2 are a transformation point temperature and a yield point temperature of the material of the first diffraction grating, and Tg3 and At3 are a transformation point temperature and a yield point temperature of the material of the second diffraction grating.
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