Nearly nondiffractive beam for lidar application

This study reports the analysis of the long distance propagation characteristics of the annular beam and its application to lidar. In our analysis, the annular beam is formed by a couple of axicon prisms. The waveform of the annular beam is transformed in to the nearly nondiffractive beam through the propagation. The propagation characteristics can be easily controlled by the waveform of the outgoing annular beam. The center peak intensity, FWHM, and the intensity ratio of the center peak intensity of the transformed nondiffractive beam to the whole beam intensity were examined in the various viewpoints. We also considered the spread and focusing angle of the annular beam, and obtained the critical angle to transform the nondiffractive beam. We confirmed that the permissible error of the optical alignment has an enough margin with the desired beam divergence. The annular beam proves its merit on a co-linear type lidar because of utilization of a large reflecting telescope with high transmitting efficiency and near distance measurement with a narrow FOV.