| 摘要 |
PROBLEM TO BE SOLVED: To reduce the leakage light from a polarizing half prism so as to suppress the occurrence of length measuring errors caused by the leakage light by adjusting the incident angle of incident light to the light splitting face of the prism. SOLUTION: In order to reduce the leakage light reflected by a light reflecting face of the polarized light component to be transmitted through the light splitting face of a polarizing half prism 3 and the leakage light transmitted through the light splitting face of the prism 3 of the polarized light component by the light splitting face, the counterclockwise rotation of the prism 3 is adjusted. Consequently, the outgoing path of a length measuring beam transmitted through the light splitting face of the prism 3 moves upward from the outgoing path before the rotation is adjusted. In addition, the returning patch of the length measuring beam totally reflected by the reflecting surface of a moving mirror 12 moves downward from the returning path before the rotation is adjusted. Therefore, the so called Abbe's condition is mostly satisfied, because the center lines of the two length measuring beams intersect the center 21 or its vicinity of a measuring probe 14, and the leakage light from the light splitting face and, accordingly, the length measuring error are reduced.
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