| 摘要 |
Optical intrument for measuring displacement comprising a movable diffraction grating used as a scale, a semiconductor laser device (1), photodetectors (10, 11) and means (2, 4, 5, 6, 7) for making two light beams diffracted by the diffraction grating interfere with eath other in which displacement of said diffraction grating is measured, based on variations of interference signals. The laser device has a suitable coherency for making selectively two necessary light beams with equal optical path lengths interfere with each other. |
