Study On Laser Attenuation Character In Atmospheric Aerosol

With the development of new laser and receiver, laser has been widely used in various fields, including industrial and agricultural production, space, national defense, etc. For instance, laser is considered as information carrier, and is employed to laser communication, target tracking, ranging, recognition, laser guided bomb, and so on. Laser is the energy source of laser weapons. Of all applications, the propagation of laser in atmosphere, which is affected by various atmospheric phenomena, must be researched.This thesis is devoted to the attenuation of laser caused by atmospheric aerosols, and some problems of laser propagation in atmosphere. It is studied the interaction of laser beam with typical aerosols, aerosols of arbitrary shape, and particle systems. The absorption, scattering and attenuation of plane waves and Gaussian beams induced by aerosols are researched. The attenuation of aerosols is employed to the laser propagation in various environments, and its application in particle sizing is also given. The influence of turbulence to light propagation is discussed, and a method of controlling scintillation is provided. Main topics include:1. Laser attenuation by typical atmospheric aerosols. Based on Generalized Lorenz-Mie Theory(GLMT), in which incident beam is expanded using vector wave function and beam shape coefficients are analytically calculated, the absorption, scattering and attenuation of various aerosols is studied, and the effect of incident beam type, wavelength, size and shape of particle, structure of particle etc to the attenuation is analyzed.2. Laser attenuation by aerosol of arbitrary shape and aerosol systems. Based on the method of moment, a model for aerosol of arbitrary shape is built, and the scattering characteristics of various aerosol, whose shape can be bi-sphere, polygon, spheroid, series of spheroid, et al, are researched. Numerical results show that absorption and scattering of aerosol depends not only on wavelength, size and refractive index, but also on the shape of particles. It is verified that the model of effective sphere will cause great error.3. The attenuation of laser in typical atmospheric aerosols. Based on the result of the attenuation of laser by single aerosol, the propagation of laser in discrete aerosol system is studied. It is discussed the effect of aerosol system with various size distribution to laser propagation, and the variation of attenuation with type of aerosol, wavelength, moisture is also analyzed. A experimental system for the measurement of concentration of aerosol is built, and the extinction of coal soot is measured using the method of extinction. The size distribution is obtained from the experimental results.4. The effect of turbulent atmosphere to laser propagation. The physical mechanism of beam expansion, beam drift, and scintillation is studied, and a mathematical model is given based on the second and fourth order of moment. A model of laser propagation in atmosphere is provided. The scintillation is studied and a model of scintillation is given. Based on such model, a way to control scintillation is discussed.