Aerosol is the main component of air pollutants. Lidar is a powerful tool to detect atmospheric aerosols. 355 nm in ultraviolet, visible spectrum and 1064 nm in near infrared are commonly used in detection, while the ultraviolet spectrum with wavelength less than 320 nm is less used. The main reason is that ozone has a certain content in the atmosphere and is strongly absorbed in the ultraviolet spectrum. Retrieving aerosol extinction coefficient from ultraviolet lidar equation is more complex than from 355 nm, visible spectrum and 1064 nm lidar equation because of the interaction of aerosol absorption, ozone absorption and atmospheric molecular absorption.The method of detecting aerosol extinction coefficient is proposed by emitting two ultraviolet lasers into the atmosphere at the same time. An iterative inversion method is designed to retrieve the aerosol extinction coefficient profile from two ultraviolet lidar equations with the ozone concentration profile as the constraint condition. In order to verify the correctness of the inversion method, the test is arranged by simulation signal.Two simulation ultraviolet lidar signals are obtained from supposed aerosol extinction coefficient and ozone concentration profiles, then, the aerosol extinction coefficient profiles in the ultraviolet spectrum are retrieved from the simulated signals by the inversion method. The results indicate that the inversion method is feasible and reliable.
Aerosol is the main component of air pollutants. Lidar is a powerful tool to detect atmospheric aerosols. 355 nm in ultraviolet, visible spectrum and 1064 nm in near infrared are commonly used in detection, while the ultraviolet spectrum with wavelength less than 320 nm is less used. The main reason is that ozone has a certain content in the atmosphere and is strongly absorbed in the ultraviolet spectrum. Retrieving aerosol extinction coefficient from ultraviolet lidar equation is more complex than from 355 nm, visible spectrum and 1064 nm lidar equation because of the interaction of aerosol absorption, ozone absorption and atmospheric molecular absorption.The method of detecting aerosol extinction coefficient is proposed by emitting two ultraviolet lasers into the atmosphere at the same time. An iterative inversion method is designed to retrieve the aerosol extinction coefficient profile from two ultraviolet lidar equations with the ozone concentration profile as the constraint condition. In order to verify the correctness of the inversion method, the test is arranged by simulation signal.Two simulation ultraviolet lidar signals are obtained from supposed aerosol extinction coefficient and ozone concentration profiles, then, the aerosol extinction coefficient profiles in the ultraviolet spectrum are retrieved from the simulated signals by the inversion method. The results indicate that the inversion method is feasible and reliable.
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.
Multiple-slit diffraction properties of high-polarization-order cylindrical vector (HCV) beams were studied in detail. Flowerlike intensity distributions are obtained after HCV beams passing through a linear polarizer. The intensity distributions of single-slit, double-slit, triple-slit and four-slit diffraction of high-order radially polarized (HRP) beams and high-order azimuthally polarized (HAP) beams are obtained, and analyzed with different slit spacings. It was indicated that diffraction fringes of HCV beams were not continuous. Faultage appeared, and the faultage number was 2P+1, which was only related to the polarization order number P, but independent of slit number N. It was found that the obvious and clear diffraction phenomenon would be obtained in the conditions 2ω≈ (N+1)D, N≥2 in which ω0 is the beam waist radius and D is the slit spacing. This study can be used to detect and analyze higher-order vector beams. Besides, it helps to design special diffractive optical elements.
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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