| 摘要 |
PROBLEM TO BE SOLVED: To decrease the number of components of a grating interference type displacement measuring instrument. SOLUTION: A fixed grating 40 and a displaced grating 42 are arranged on the optical path between a coherence light source 10 and a photodetecting element 44 and a prism 41 is arranged between the two gratings. The incidence surface and projection surface of the prism 41 are not parallel, but contain a specific tilt angleγ. The light from the coherence light source 10 is split by the fixed grating 40 into diffracted light and transmitted light. The diffracted light is refracted by the prism 41, diffracted by the displaced grating 42, and transmitted through the prism 41 and fixed grating 40 again to impinge on the photodetecting element 44. The transmitted light is diffracted by the prism 41 and by the displaced grating 40 to impinge on the photodetecting element 44. The two pieces of luminous flux which are made incident on the photodetecting element 44 are put one over the other at a certain angle because of the prism 41 to form interference fringes. The photodetecting element 44 detects the interference fringes to measure the displacement.
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