| 摘要 |
A diffractive optical element including a first layer made of a first optical material having high refractive index and low dispersion, and a second layer made of a second optical material having low refractive index and high dispersion. The first and second layers are stacked together. The outer surfaces of the first and second layers are substantially smooth, while the connecting surfaces of the first and second layers are substantially contoured to follow a relief pattern. To satisfy a preferred operating wavelength range of 400 nm to 700 nm, a glass selected from the group consisting of BSM7, BSM81, BSL7, BAL5, BAL50, BAL22, LAL11, LAL12, LAL18, YGH51, LAH57 and LAH75 may be used as the first optical material, and a silicate glass containing certain amounts (e.g., 2 to 25 mol %) of Tl2O may be used as the second optical material.
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