| 摘要 |
PROBLEM TO BE SOLVED: To provide a length meter that is hardly affected by changes in thickness of an optical window on a measurement optical path due to environmental changes, in measurement of length using an interferometer. SOLUTION: A vacuum tube 10, the inside of which is kept in a vacuum state, having optical windows 10b and 10c at both ends thereof is disposed on a measurement optical path. Each of the optical windows 10b and 10c has two parts having a difference in thickness. A measurement beam of a laser beam 2a for measurement of length is incident on a part of the two parts of the optical window 10b and a part of the two parts of the optical window 10c. A measurement beam of a laser beam 2b for measurement of length is incident on the other part of the two parts of the optical window 10b and the other part of the two parts of the optical window 10c. The measurement beams are reflected by a measurement mirror 5 and then interfered with reference light from a reference mirror 6. Two values of the measured length obtained by using the laser beams 2a and 2b for measurement of length are used for, thereby measuring length without the influence of changes in length of the optical path caused by changes in thickness of the optical windows 10b and 10c due to environmental changes. COPYRIGHT: (C)2012,JPO&INPIT |
