| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect the interference maximum value by providing a device for generating a frequency shift between two interfering partial beams on a beam path of a first partial beam and/or a beam path of a second partial beam, and providing a beam splitting device in front of a photodetector on a beam path of interference light. SOLUTION: A collimated beam is split into a first partial beam, a second partial beam 3 or a partial beam 4 in a first beam splitter ST1. The partial beam 3 is distributed on the surface of a measuring object 7 through a focusing lens 6, and after reflection, it reaches the splitter ST1. The second partial beam 4 is guided to acousto-optical deflectors 8, 9 through a reflector SP. The deflectors 8, 9 are controlled by a driving unit 12. By frequency modulation, the deflecting angle of the beam 4 is changed by an angleαin the deflector 8, and again deflected in the deflector 9 to be moved in parallel. Further the beam is reflected and diffracted by diffraction grating 10 to again return to the splitter ST1, so that the beam 4 is superposed on the return beam 3 to interfere with each other.
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