A coherent dual-frequency lidar architecture for long-distance high-precision ranging and velocity measurement is proposed, using the method of optical heterodyne detection, which can avoid complex optical coherence configurations. The system uses a dual-frequency laser with a beat frequency of 200MHz as the dual-frequency light source, and performs measurement through the principles of phase ranging and Doppler velocimetry. The experimental verification shows that the operating distance of the system reaches 3200m, the distance resolution is less than 0.5m, and the speed measurement accuracy range is ±0.25m/s. The results show that the system can realize long-distance high-precision single-point ranging and speed measurement.
Spatial patterns are a significant characteristic of lasers. The knowledge of spatial patterns of structured laser beams is rapidly expanding, along with the progress of studies on laser physics and technology. Particularly in the last decades, owing to the in-depth attention on structured light with multiple degrees of freedom, the research on spatial and spatiotemporal structures of laser beams has been promptly developed. Such beams have hatched various breakthroughs in many fields, including imaging, microscopy, metrology, communication, optical trapping, and quantum information processing. Here, we would like to provide an overview of the extensive research on several areas relevant to spatial patterns of structured laser beams, from spontaneous organization to multiple transformations. These include the early theory of beam pattern formation based on the Maxwell–Bloch equations, the recent eigenmodes superposition theory based on the time-averaged Helmholtz equations, the beam patterns extension of ultrafast lasers to the spatiotemporal beam structures, and the structural transformations in the nonlinear frequency conversion process of structured beams.
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