| 摘要 |
PROBLEM TO BE SOLVED: To measure the amount of a dead path and to decrease the dead path in a heterodyne interferometer having a plurality of laser beams with slightly different wavelengths as a light source. SOLUTION: The heterodyne interferometer comprises: a laser light source 1 emitting a plurality of the laser beams with slightly different frequencies; phase detecting units 7, 8 splitting the laser beams emitted from the laser light source into a reference light beam and a measuring light beam, allowing the reference light beam reflected by a reference mirror and the measuring light beam reflected by an object to be measured to interfere with each other, and detecting a phase in each frequency of interfered light; a displacement calculating unit 9 calculating a displacement of an equivalent wavelength from the detected values of the phase detecting units; an optical path length difference calculating unit 9 calculating the optical path length difference between the reference light beam and the measuring light beam from the calculated displacement and the displacement of the equivalent wavelength corresponding to phase values providing zero phase difference of the interfered light in each frequency calculated backward from the detected values of the phase detecting units 7, 8; and an optical path length adjusting mechanism 4 adjusting at least either the optical path length of the reference light beam or the optical path length of the measuring light beam depending on the detected optical path length difference. COPYRIGHT: (C)2004,JPO
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