Wave Front Twist Of A Laser Beam Propagation In An Atmospheric Turbulence

The random refractive-index fluctuations of atmospheric turbulence disturb and result the fluctuations of the beam wavefront and amplitude of a light wave propagation through the atmosphere that cause a number turbulent effects, such as scintillations and beam wander etc., which effect seriously on the beam quality of wave propagation in atmosphere and the behaviors of an optical system under atmosphere, such as laser radar and laser communication (lasercom). The model of random refractive-index fluctuations of atmospheric turbulence is a base of theoretical study and experimental analyses for the turbulent effects of wave propagation in turbulent atmosphere.In the First part of this dissertation, we develop a relatively simple two-scale model of the refractive-index fluctuations which include the outer-and inner-scale of turbulence , under the following three approximations: The modulation of turbulent atmosphere on propagating wave is a two-scales modulation process in which the fluctuations caused by small-scale eddies are multiplicatively modulated by the fluctuations which are caused by large-scale eddies. The modulations of the small- and large-scale eddies, respectively, are statistically independent. The Rytov method for optical scintillation is valid even into the saturation regime with the double-scales modulation model. Base on the model of the refractive-index fluctuations which is obtained by ourselves, we study the effects of the turbulent inner- and outer-scale on the aperture-averaging factor of optical scintillations for the plane wave, spherical wave and Gaussian-Schell beam propagating in the turbulent atmosphere. We have shown that the size of aperture, the inner- and outer- scale and wavelength of wave source are factors, which shall consider in the measurement and analyses of optical scintillation. We have also shown that the turbulence outer-scale which reduces the aperture-averaging of scintillations for Gaussian-Schell beam propagation in weak-scintillation atmospheric turbulence. In addition, we study the effects of the inner- and outer-scale of the turbulence on the integral resolution of a simple system of imaging through the atmosphere and Fried coherence- parameter .We have shown that the finite outer-scale of the turbulent atmosphere is an important factor that affects the integral resolution of a large aperture system of imaging,...