| 摘要 |
PROBLEM TO BE SOLVED: To provide a length measuring instrument enabling reduction in errors in a measured length value due to a change in a refractive index of air. SOLUTION: This length measuring instrument is equipped with a laser interference length measuring instrument for separating laser light 12 outputted from a laser light source 9 into reference light B and length measurement light A to measure the length of an object under inspection by using interference between the reference light B and the measurement light A. An etalon 10 is disposed in the vicinity of an optical path of the reference light B, with the etalon 10 entered by laser light C and having the same optical path length as that of the optical path of the reference light B. A change in the optical path length L2 of the reference light B is corrected by an optical path length L3 of the etalon 10. COPYRIGHT: (C)2007,JPO&INPIT
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