双程湍流大气中粗糙目标对拉盖尔高斯涡旋波束的散射特性研究

The study on characteristics of laser beam scattered by rough surface has been one of the closely-watched foremost subjects. The paraxial approximation theory is not entirely applicable to the propagation of vortex beams with wide divergence angles under high topological charge, so the nonparaxial propagation theory of vortex beams become an urgent research topic. Based on the expansion method of Gaussian beams, we investigate the light field description, intensities, amplitudes, as well as polarization of the Laguerre Gaussian (LG) vortex beam propagation in atmospheric turbulence, explore the problem of OAM conservation in vortex beams through atmospheric turbulence. Using the extended Huygens Fresnel principle, the field model of the LG vortex beams scattered by rough targets in turbulent atmosphere along double paths is established, the second-order and fourth-order moments of the scattering fields are build, the problem of multiple integral simplification of the fourth-order moment in the scattering field is solved, the characteristics of intensities, polarization and intensity scintillation of the fields scattered by rough targets are studied, the effects of target parameters and turbulence level on the target scattering characteristics are analyzed, the related physical mechanisms are revealed. The phase screen approximation method for scattering fields from various types of target is proposed to simulate the propagation and scattering from rough targets of the LG vortex beam in the atmospheric turbulence. It provides theoretical basis and technical support for the applications of target detection and recognition, laser communication, laser radar and laser guidance.

粗糙表面对激光的散射特性研究一直是备受关注的前沿课题之一。由于傍轴近似理论不完全适用于高拓扑荷下宽发散角涡旋光束的传输，因此涡旋光束的非傍轴传输理论是亟待研究的课题。本项目基于高斯子波束展开法，研究湍流大气中拉盖尔高斯涡旋光束单程传输的光场描述，及强度、幅度、偏振特性，探索涡旋光束经湍流大气传输后轨道角动量是否守恒。采用广义惠更斯-菲涅耳原理，建立双程湍流大气中粗糙目标对拉盖尔高斯涡旋光束的散射场模型，建立散射场的二阶、四阶统计矩，解决散射场四阶矩多重积分化简的难题，研究粗糙目标对拉盖尔高斯涡旋光束散射的强度、偏振及强度闪烁特性，分析目标特征参数及湍流强度对目标散射特性的影响规律，揭示相关的物理机理。提出多种类型目标散射场的相位屏近似方法，数值模拟湍流大气中拉盖尔高斯涡旋光束的传输及粗糙目标散射特性。研究成果为空中目标探测与识别、激光通信、激光雷达、制导等应用提供重要的理论依据及技术支撑。

基于高斯子波束展开法，建立了符合非傍轴传输的拉盖尔高斯涡旋波束的单程传输理论模型，研究拉盖尔高斯涡旋波束经湍流大气传输后到达接收面处的强度、相位的变化规律，探索OAM分布特性，并给出物理机理描述。基于Rytov近似理论及广义惠更斯-菲涅耳原理，建立了湍流大气中普通激光束的有限尺寸粗糙目标散射场的四阶统计矩模型，推导了接收面处强度协方差和闪烁指数，研究了“目标孔径”效应，并给出了散射特性的物理机理描述。基于Rytov近似理论，解决了湍流大气中涡旋光束目标散射场四阶矩多重积分的化简难题，得到散斑相干长度及闪烁指数数学模型；研究了湍流大气中随机粗糙面目标对拉盖尔-高斯涡旋光束的回波散斑特性，并与高斯波束进行了比较，揭示了粗糙目标尺寸、粗糙度及湍流强度对散射特性的影响规律。基于分步傅里叶算法，数值模拟研究了湍流大气中Airy和BG涡旋光束的自修复和无衍射特性，并将两种光束的两种特性进行了比较。将分步傅立叶算法推广到双程湍流大气目标散射场模拟中，数值模拟研究了多种类型目标对普通激光束回波的相干长度、强度闪烁特性；分析了目标特征参数、湍流强度对散射光场的影响。基于激光动态散斑时频信号，建立了一套适用于角反射器阵列的微动参数反演算法；实验测量了旋转粗糙目标的时间相关函数，建立了粗糙目标散斑时－空相关函数简化模型并与理论结果进行了对比。研究成果在湍流大气中目标探测与识别、激光制导、通信、激光雷达信息提取以及散斑测量技术等领域有重要的的理论价值和广泛的应用前景。