High-precision measurement method of laser divergence angle based on interference and micro-focusing

Laser beam divergence angle is an important parameter of laser load, which is of great significance in the field of spaceborn LiDAR. A smaller laser divergence angle can effectively provide energy utilization and reduce the distance measurement error, especially in high-precision laser ranging and remote sensing applications, where the divergence angle of the laser beam needs to be controlled within a very small range to ensure the accuracy and reliability of LiDAR. Therefore, it is particularly important to accurately measure the laser far-field divergence angle. In this paper, we propose a composite measurement method, which integrates interferometry and micro-imaging technology, to address the problem that the divergence angle of spaceborn LiDAR is better than 20μrad and the measurement accuracy is very high. A high precision calibration system is composed of a microscopic camera and an interferometer, and the influences of the detector, the collimator and the positioning accuracy of the focal plane on the divergence angle measurement are deeply analyzed, and the focal plane is calibrated with high precision according to the wavefront measurement data of the interferometer, so as to realize the high-precision positioning of the detector position. A divergence angle test system consisting of a 20m focal length collimator and a detector is established, which successfully realizes the high-precision measurement of laser far-field divergence angle, and the results of the error analysis show that the measurement accuracy of this method is better than 0.61μrad, which can satisfy the test requirements of LIDAR, and it has an important value for engineering applications in the fields of remote sensing and LIDAR.