Feedback gain adjusting method and device of tracking-type laser interferometer and tracking-type laser interferometer

A feedback gain adjusting device of a tracking-type laser interferometer, the tracking-type laser interferometer comprising:

• a laser interferometer;
• a position sensitive detector configured to detect an offset of an optical axis of the laser interferometer;
• a biaxial rotator configured to turn the laser interferometer toward an arbitrary direction;
• an angle sensor configured to detect a rotation angle of the biaxial rotator;
• a retro reflector configured to reflect reflected light in a direction parallel to incident light;
• and
• a controller configured to perform feedback control of the biaxial rotator so as to track the retro reflector based on signals from the position sensitive detector and the angle sensor, wherein:
• tracking control is started when return light from the retro reflector is returned to a detection range of the position sensitive detector, and
• gain for the feedback control is changed in accordance with a behavior for a position of the return light on the position sensitive detector due to the tracking control.

A tracking-type laser interferometer comprising:

• a laser interferometer;
• a position sensitive detector configured to detect an offset of an optical axis of the laser interferometer;
• a biaxial rotator configured to turn the laser interferometer toward an arbitrary direction;
• an angle sensor configured to detect a rotation angle of the biaxial rotator;
• a retro reflector configured to reflect reflected light in a direction parallel to incident light;
• and
• a controller configured to, when feedback control is performed on the biaxial rotator so as to track a behavior of the retro reflector based on signals from the position sensitive detector and the angle sensor:
• start tracking control when return light from the retro reflector is returned to a detection range of the position sensitive detector, and
• change gain for the feedback control in accordance with a behavior for the position of the return light on the position sensitive detector due to the tracking control.