| 摘要 |
PROBLEM TO BE SOLVED: To improve precision of angle measurement by measuring an incident angle of a laser beam to a reflection unit when an amount of rotation is measured by using a laser interfrometer. SOLUTION: A beam interference synthesizing unit 2 is fixed to a part independent of rotation of a table 20. A reflecting means 5 for angle detection is fixed to an angle rotation mechanism 10 which rotates around the rotation shaft as a center which shaft is fixed to the table 20. Setting is so performed that a laser beam enters the reflecting means 5 at an initially set incident angle. When the table 20 is rotated by 1/N, change of difference of the optical length of a laser interferometer is measured and stored. When the angle rotation mechanism 10 is rotated in the opposite direction, change of difference of the optical length is measured and stored. These operations are repeated until the table accurately makes one revolution. From the change of difference of the measured optical path length, the initially set incident angle is calculated.
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