| 摘要 |
A dichroic mirror made of at least ten or more alternate high refractive index and low refractive index layers for a designed wave length expressed by lambda o, basic optical film thickness of the high refractive index layers are represented by 1/4 lambda o and 3/4 lambda o, while the basic optical film thickness of the low refractive index layers is represented by 1/4 lambda o. Thickness of the first layer, the second layer and the last layer as counted from a substrate, also of at least one layer of other intermediate layers are shifted from the basic optical film thickness, so that properties of the mirror are improved and a production thereof is made easier.
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