Detection and active stabilization of beams position at a high-resolution laser interferometer

In metrology applications of laser interferometers like a scale calibration of capacitive or inductive sensors, strictly linear positioning of the measuring mirror of the interferometer is necessary. It is maintained usually by a stage, which is based on principle of linear guide ways with ball carrier bearings. But possible imperfection of guides of the travel stage can cause deviations of the mirror plane from the right angle to the axis of traveling. Mentioned angle deviations lead to distortion of interference fringes in the output of the interferometer and by other words it causes non-linearity of the interferometer scale. Because the phenomenon is very random for this type of the travel stage the uncertainty of calibration of sensors is higher. In the work we present a method, which eliminates this usual problem by two ways. The first of them utilizes a special configuration of the laser interferometer where possible angle deviation of the mirror plane is compensated by second pass of the laser beam in the measuring arm of the interferometer. The next way is based on continual monitoring of spatial position of laser beams in the interferometer when the measuring mirror is positioned. It works with condition that the mirror can be slightly tilted by piezoelectric actuators in servo-loop mode with respect to detected spatial position.