| 摘要 |
PURPOSE: To correct measurement errors attributed to the alteration of refractive index of an optical path and carry out highly precise measurement with lowered cross-talk by providing optical path separating means to separate an optical path for light rays to be measured and an optical path for reference light rays mutually spatially. CONSTITUTION: Light rays with frequencyω2 and light rays with frequencyω3 which pass a reference optical path and come out of a deflecting beam splitter 4 and light rays with frequencyω2 andω3 which pass an optical path for light rays to be measured and come out of the beam splitter 4 go along mutually different optical paths and enter a frequency separating element 7. Light rays with frequencyω2 andω3 are separated from light rays (light rays with near frequencyω1) from a light source 12 for light rays to be measured. The reference light rays reflected by a fixed mirror 5 and light rays to be measured which are reflected by a moving mirror 6 are received along mutually different optical paths. That is, light rays with frequencyω2,ω3 which go along the optical path for light rays to be measured and light rays with frequencyω2,ω3 which go along the optical path for reference light rays are not overlapped mutually and detected independently. As a result, the cross-talk for correction of the alteration of refractive index can be avoided.
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