| 摘要 |
PROBLEM TO BE SOLVED: To provide a dark-field-type autocollimator, capable of easily reducing ghost lights caused by reticles for projecting light. SOLUTION: The reticle 2 for projecting a light is subjected to dark-field illumination, and the scattering light from a first reticle pattern is guided to an object lens 4 via a beam splitter 3, collimated at the object lens 4, and projected to an autocollimator mirror M. The reflected light is projected to a fixed reticle 5, provided with an illuminated second reticle pattern via the object lens 4 and the beam splitter 3. Here, since the difference in the refraction of the refractive-index interface between a reticle substrate 21 and glued layer is equal to 0.1 or smaller and the refraction difference of the refractive-index interface between an absorbing plate 22 and a glued layer is also equal to 0.1 or smaller in the reticle 2 for projecting light, illuminating light is hardly reflected at both reflective-index interfaces. Therefore, it is possible to easily prevent the occurrence of ghost images caused by reflection at the refractive- index interfaces, in the vicinity of the reticle patterns provided for the reticle 2 for projecting light.
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