Laser tracking interferometer

A laser tracking interferometer for detecting a displacement of a first retroreflector by utilizing interference of a laser beam emitted toward the first retroreflector as a measured body and reflected by the first retroreflector in a return direction, the laser tracking interferometer performing tracking by using a positional change of an optical axis of the laser beam, the laser tracking interferometer comprising:

• a reference sphere fixed in place;
• a carriage having a first displacement gauge configured to output a displacement signal associated with a relative displacement between the first displacement gauge and the reference sphere;
• a second retroreflector provided on the carriage;
• a laser interferometer configured to output a displacement signal associated with a relative displacement between the first retroreflector and the second retroreflector;
• a displacement measurer provided on the carriage and configured to measure an amount of change in a distance between the first displacement gauge and the second retroreflector;
• and
• a data processor configured to calculate a displacement of the first retroreflector with reference to the reference sphere based on the displacement signal output from the first displacement gauge, the displacement signal output from the laser interferometer, and the amount of change measured by the displacement measurer.