| 摘要 |
Interferometric apparatus for measuring changes in altitude between a surface and a datum line where the apparatus comprises a dimensionally stable metrology frame and the datum line is defined in an object mounted for nominally plane translation with respect to the metrology frame in at least two orthogonal directions while experiencing relatively smaller changes in altitude in a direction nominally normal to at least two orthogonal directions. An elongated reflector is mounted with respect to either the metrology frame or the object to provide the surface, and at least one interferometer system is mounted at least in part on object for movement therewith. The interferometer system is structured to provide a measurement beam that travels along at least one optical path to and from the elongated reflector to provide a signal containing information that varies in accordance with changes in altitude between the surface and the datum line as the object moves, and is configured so that the signal is insensitive to variations in angular rotation of the object at least about one of the two orthogonal directions.
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