Three-degree-of-freedom common-path laser measurement system

Abstract

Common optical path arrangement was adopted to design a three-degree-of-freedom laser measurement system for measuring 1D displacement and 2D angles of a moving stage simultaneously on the basis of the principles of Michelson interference and laser auto-collimation. In the displacement measurement, the fine resolution of displacement measurement was achieved by using optical path difference doubling technique. Combined with polarization interference technology and signal differential processing, high-quality displacement output signal was obtained. In the angle measurement, changes in yaw and pitch of a moving stage caused the position change of the mirror which was mounted on the stage. The incident beam was reflected by the mirror and detected by a four-quadrant detector. According to the position change of the spot, yaw and pitch angles were obtained. The stability, resolution tests and the comparison experiments with the British Renishaw XL-80 laser interferometer were done. Experimental results show that the system has the resolution of 0.8 nm for displacement measurement and 0.2″ for angle measurement. Compared with the results of Renishaw XL-80 laser interferometer, the maximum deviation of displacement is less than 100 nm within the measurement range of 50 mm. The maximum deviations of yaw and pitch are 0.5″ and 0.4″.