| 摘要 |
An interference filter for use in a copying machine comprises a glass substrate and a plurality of high-refractive index and low-refractive index layers alternately superposed on the substrate for reducing ripples at opposite sides of the reflective range. The first and second layers counted from the substrate have a greater optical layer thickness than lambda o/2. The third and fourth layers have a greater optical layer thickness than lambda o/4. The second top layer has a greater optical layer thickness than lambda o/2. The top layer has a smaller optical layer thickness than lambda o/4. The remaining layers have an optical layer thickness equal to lambda o/4.
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