Laser Beam Propagation On The Slant Path Through The Turbulent Atmosphere And The Characteristics Of Returned Waves By Targets

Laser propagation in the turbulent atmosphere is one of important research topics of latter-day optics and its engineering application, and is significant for laser satellite-Earth communication, target characteristic extracting and calibrating, laser tracking, controlling and guiding.The topic of laser beam propagation on the slant path through the atmospheric turbulence and the characteristics of returned waves by targets have great value.The main topics and results are as follows:First, the transmitter and receiver parameters become apparent in the derived analytical expressions for the log-amplitude variance of the Gaussian beam propagation on the slant path. The expressions verify general optical turbulence-related characteristics predicted for Gaussian beams, provide additional insights into beam-wave behavior, and are convenient tools for beam wave analysis and can be reduced to a Gaussian beam wave model on horizontal sight paths of invariable C_n~2. The numerical results of different form beam log-amplitude variance with the height of receiver, Fresnel zone size and receiver parameters are given.Second, by adding a non-Gaussian correction to the Gaussian solution to the m + mth order moment equation under complete saturation case, an analytical solution is deriveded for general strong scattering regime. The Gaussian term is the sum of the product of the second order moment, while the equation for the non-Gaussian part can be treated by Rytov approximate method. Based on the theory frame and the solution method of analytical solution, the fourth and eighth moment are obtained when wave propagation in the turbulent atmosphere.The equation for higher-order moment has been treated without restrictions on both the scattering regimes and incident wave sources, thus the analytical solution is general. Finally, the relation of the plane wave scinllation index with turbulent intensity, zenith angle and propagation distance are discussed.Third, on slant paths, by applying a modification of the Rytov method, a tractable model is developed for the scintillation index of a Gaussian optical beam wave that is valid under moderate-to-strong irradiance fluctuations considering inner- and outer- scales effects of turbulence. The results agree with experimental scintillation. This scintillation model can be converted into a plane or a sphere wave scintillation index model on slant paths, and also reduced to a Gaussian beam wave model on horizontal sight paths of invariable C n2. According to Huygens-Fresnel and Mellin transform techniques, spreading radius and wander with outer scale effect on the slant path, and applying the ITU-R C_n~2 model which is altitude dependent to calculate the spreading radius and wander covariance with different height of drone in the slant path. These results can be reduced to a Gaussian beam wave model on horizontal sight paths of invariable C_n~2.Fourth, the extended Huygens-Fresnel principle is utilized to make analysis of the backscattering of a target in the turbulent atmosphere. The treatment includes the effects of the atmospheric turbulence both on the laser beam as it propagates to the target and on the scattered field as it propagates back to the receiver. The covariance function and variance of the scattering intensity are derived with considering the fluctuation of the log-amplitude and phase, and the numerical results are given. The influence of wavelength and propagating distance on the covariance function and normalized variance of the scattering is discussed. The statistical effects of the atmospheric turbulence on coherent radiation scattering from a diffused target are extended to the target with multiple glint (the glint is small compared with the illuminating beam). The influence of radius of the glint and the distance off the incident beam on these parameters is discussed.Finally, based on the Rytov theory and rotationally symmetric ABCD ray matrices, this paper educed the mutual coherence function, mean intensity and scintillation of retuned waves by plane mirror and retroreflector in the turbulent on the slant path, and can be reduced to model on the horizontal path of invariable C n2. The results of Gaussian beam, spherical wave and plane wave incident on plane mirror and retroreflector are discussed respectively.