Atmospheric detection is the basis of air pollution control, lidar is a powerful tool for atmospheric detection. Because of blind area and transition area, lidar cannot get complete echo signals in the near range. Laser beam imaging technique based on charge coupled device (CCD) can solve the above difficulties caused by lidar effectively. Laser beam imaging technique is studied from theoretical analysis and simulation experiment, including imaging characteristics, the angle relationship between CCD image plane and lens plane, the influence of laser beam divergence angle on detecting spatial resolution. The comparison experiments show that laser beam imaging technique in detecting atmospherics is reliable and feasible. Furthermore, the application cases are given in detecting aerosol backscattering coefficient, aerosol extinction coefficient, aerosol phase function and PM2.5 mass concentration
Aerosol extinction coefficient profile is an essential parameter for atmospheric radiation model. But it is difficult to get the full aerosol extinction profile from the ground to the tropopause especially in near ground precisely using backscattering lidar. A combined measurement of side-scattering, backscattering and Raman-scattering lidar is proposed to retrieve the aerosol extinction coefficient profile from the surface to the tropopause which covered a dynamic range of 5 orders. The side-scattering technique solves the dead zone and the overlap problem caused by the traditional lidar in the near range. Using the Raman-scattering the aerosol lidar ratio (extinction to backscatter ratio) can be obtained. The cases studies in this paper show the proposed method is reasonable and feasible.
Vortex beams with integral and fractional topological charges are generated by an experimental setup with one phase-only liquid crystal spatial light modulator which efficiently modulates the phase retardation distributions of input beam. The intensity distributions and double-slit interference of vortex beams with integral and fractional topological charges are investigated in detail. Tilt appears in double-slit interference fringes of vortex beams. The fringe tilt amounts in the intermediate region are proportional to the topological charge l of vortex beams. The double-slit interference method can be utilized to determine the topological charge of vortex beams.
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