| Space laser communication has high demand for communication quality and stability. In the choice of signal emission source, semiconductor pumped solid-state laser has advantages of concise structure, long service life and high efficiency, and outgoing laser beam has characteristic of high output power, high beam quality and high stability. In the range of solid-state laser, slab laser is the best choice because of its excellent heat-conducting property.As shown below, the present paper studied on the characteristic of slab solid laser outgoing beam in theory and experiment, including beam divergence angle, beam waist radius and far-field facula form:(1) An overview of the general situation of slab laser and space laser beam reshaping, reviewed the advantage and state of development of slab laser, beam reshaping and space laser beam transfer study.(2) Introduced beam transfer characteristic method (mainly on optical transfer matrix) and fundamental mode Gaussian beam description, quality evaluation and application on ABCD law.(3) Analyzed Mie scattering caused by atmospheric particle, including theory basis of Mie scattering in monodispersive system and the effect of particle form, scale parameter, refractive index on scattering. Exposed the theory and computing method of intensity distribution function, volume scattering function, scattering cross-section and efficiency factor.(4) Reshaped the elliptical far field facula of Gaussian beam of slab solid-state laser in theory and experiment. First, according to the definition of diffraction limit times and reshaping requirements, geometric method was used to design the reshaping system. Second, analyzed the ABCD law of Gaussian beam, selected five groups of cylindrical concave and convex lens of different focal lengths and simulated cylindrical telescope system to expand the x-scale of ellipse beam and single wavelength beam expanding system to compress the x-scale and y-scale of far-field divergence angle. The result was that the x-scale initial divergence angle of 600 ?rad could be compressed to 230 ?rad if the specified cylindrical lens focal length were chose, in the meanwhile both of the x-scale and y-scale beam waist position were same. Then beam expander was used to expand the x-scale and y-scale beam which got the far-field divergence angle of 76.7 ?rad in x-scale and 83.3 ?rad in y-scale. Final, the experimental result was that in contrast to simulation, the beam far-field divergence angle was 92.8 ?rad in x-scale and 107.0 ?rad in y-scale.(5) An exploration was carried out to solve the problem of facula form in CCD receiver caused by Mie back scattering when Gaussian beam was transferred in atmosphere, respectively in theory and experiment. First, the Beer law of atmosphere laser transmission and the scattering intensity function of Mie back scattering were analyzed. Second, the formula of position and radius of facula center in CCD receiver were deduced. Third, the atmosphere layering model was built so that Gaussian beam could be divided into several layers which could be imaged in CCD receiver. Fourth, the total intensity of back scattering facula could be calculated by overlaying the layered facula which was found in direct proportion to atmospheric particulate concentration. In experiment, the basic parameters of outgoing beam were controlled to remain unchanged to measure the Mie back scattering image in CCD receiver in different atmospheric particulate concentration. The experimental image and simulated image were compared which built basics of studying other laser beam transmission through back scattering. |
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