Patent ID: 7388674

Claim:
A laser tracking interferometer which directs a laser beam to a retroreflector serving as an object to be measured to sense a displacement of the retroreflector using interference with a laser beam back reflected from the retroreflector and to track the retroreflector using a change in position of the optical axis of the laser beam, the laser tracking interferometer comprising: a reference sphere disposed at a fixed location; a carriage configured to rotate about a center of the reference sphere; a laser interferometer for providing a displacement signal corresponding to a displacement of the retroreflector, and a displacement gage for providing a displacement signal corresponding to a relative displacement between the reference sphere and the displacement gage, the laser interferometer and the displacement gage being disposed on the carriage; a data processing apparatus for computing a displacement of the retroreflector with respect to the reference sphere in accordance with the displacement signal provided by the displacement gage and the displacement signal provided by the laser interferometer; position sensitive detector for providing a position signal corresponding to the amount of deviation of a laser beam when the laser beam is reflected off the retroreflector back into the laser interferometer and deviated in a direction orthogonal to its optical axis; and control means for controlling rotation of the carriage based on the position signal from the position sensitive detector so that the amount of deviation becomes zero.