| 摘要 |
<p>The structure of the optical system of this detection is simple, and the adjustment of this system is easy. The detection range is wide, and the resolution is high. The positional shift in a plane can be detected, and at the same time, the gap between two objects can be detected directly, stably, and continuously even in exposure. Two pairs of monochromatic beams having a slightly different frequencies are used. The beams are directed to diffraction gratings, or first and second objects, by allowing them to shift to the left and right, respectively, on both sides or one side of the optical axis. A plurality of beams of diffracted rays interfered by optical heterodyne emerge from positions symmetrical to the optical axes. The beams of diffracted rays thus formed are allowed to interfere so that one or more beat signals is produced in each pair. The phase variations of the beat signals between the pairs or in the pairs are determined. Hence the positional shift and gap between the two objects are detected at a time by the sum of and difference of the phase variations.</p> |
