| 摘要 |
PURPOSE: To easily obtain a movement data of high resolution while avoiding a collision of a first and a second scales, by setting a distance between a phase grating and an amplitude grating to satisfy a specified condition when the relative displacement data of the first and second scales is obtained. CONSTITUTION: The luminous flux emitted from a light source LGT is turned to a parallel luminous flux R by a collimator lens CL and shed onto a first scale D. A transmitting-type phase grating GT1 is recorded on the scale D. The luminous flux entering the phase grating GT1 is diffracted and made incident on a second scale having amplitude gratings GT2A-GT2D. Interference lights based on diffraction lights diffracted at the amplitude gratings GT2A-GT2 D are detected by a photodetecting means S comprising photodetecting elements SA, SB, SC, SD. When a relative displacement data of the first scale D and the second scale is to be obtained, the distance (h) between the phase grating GT1 and the amplitude grating GT2A-GT2D is set to satisfy (Pl<2> -4λ<2> )/(8λ)<h.
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