Development of the calibration method for multiwavelength beam coaxiality of femtosecond laser tracker

Abstract. Visible light and infrared light, included in a femtosecond laser tracker, have been widely employed for precise orientation and high-precision ranging measurements of targets, respectively. In the above measurement process, it is always necessary to ensure the coaxiality of those two laser beams with different wavelengths. According to the structural characteristics of the instruments, a calibration method for the coaxiality of tracking light and femtosecond ranging light of the femtosecond laser tracker based on frequency doubling crystal is proposed, which is the detection of the coaxiality deviation caused by the included angle between the beams. We investigate the principle of two-beam laser coaxiality detection and calculate the parameters of the system. The detection system is further developed, and the error analysis is carried out. The results demonstrate that the tracking laser and femtosecond laser is coaxial within an accuracy of 1.5 arc sec, satisfying the measurement requirements.