Optimum Design of Synthetic-Wave Absolute-Distance Interferometer Using Two-Cavity Dual-Frequency Nd:YAG Laser

The experimental set-up of the synthetic-wave absolute-distance interferometer has been briefly introduced, which employs the two-cavity dual-frequency Nd:YAG laser (TCDFL) frequency-stabilized by the quadrature-demodulated Pound-Drever-Hall (QD-PDH) method. The main error factors influencing the accuracy of absolute-distance measurement have been theoretically analyzed, and an optimized design scheme of the synthetic-wave absolute-distance interferometer has been proposed, in which a TCDFL at 1064 nm with a frequency difference of 24 GHz stabilized by the QD-PDH method is employed as the light source to construct a Mach-Zehnder interferometer. The phase difference between the two heterodyne interference signals varies by 360° when the reference retroreflector is displaced by a half of synthetic wavelength, and such a relationship can be used to calibrate the magnitude of synthetic wavelength in air under the measurement environment conditions. The phase difference between the two heterodyne interference signals can be determined by means of the quadrature phase-shift method so that the fractional order of the synthetic-wave interference fringe can be obtained when the measuring retroreflector is positioned at both ends of the measured absolute-distance, respectively. The integer order of the synthetic-wave interference fringe can be uniquely determined by an initial estimation for the measured absolute-distance on the condition that the initial estimation uncertainty is less than a quarter of the synthetic wavelength. The absolute-distance measurement uncertainty has been theoretically analyzed, laying a solid foundation for the research and development of the high-accuracy synthetic-wave absolute-distance interferometers.