Identification and elimination of half-synthetic wavelength error for multi-wavelength long absolute distance measurement

A multi-wavelength absolute distance measurement method based on synchronous occurrence and phase measurement of coarse and refined synthetic wavelength is proposed to remove the effect of vibration on the measurement distance. The phase value of refined synthetic wavelength is monitored to see if half-synthetic wavelength error occurs by judging whether it is near to 2π or 0. If yes, a new suitable refined synthetic wavelength is generated to re-measure the distance with phase near π. A measuring system has been built with a He–Ne laser source and three acousto-optic frequency shifters for implementation of this method. A comparative measurement has been performed using a counting laser interferometer at a distance of 20 m. Actual measurements indicate that half-synthetic wavelength error has been identified and eliminated with uncertainty of smaller than 60 µm under laboratory conditions.