各向异性部分相干光束空间传输特性研究
文献类型：学位论文
| 作者 | 张荣 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 王向朝 |
| 关键词 | 部分相干光束 湍流大气 光束传输 空间相干 偏振分布 光强分布 |
| 其他题名 | Research on the propagation properties of anisotropic and partially coherent beams |
| 中文摘要 | 部分相干光束具有发散角小和抗大气湍流影响能力强的特点，已逐步应用于激光雷达、自由空间激光通信等领域。在这些领域，合理选择光束模式及光源参数必须了解部分相干光束空间传输特性。目前部分相干光束空间传输特性研究主要局限于各向同性光源产生的各向同性部分相干光束，各向异性部分相干光束传输特性研究偏少。实际上部分相干光源产生的光束通常是各向异性部分相干光束。现有研究不能准确地描述实际光束空间传输特性，特别是具有各向异性空间相干分布和复杂偏振分布的部分相干光束的传输特性。基于上述考虑，本论文采用典型的各向异性高斯-谢尔模型光束，研究了各向异性部分相干光束自由空间及大气中的传输特性。主要研究工作包括： 1．提出了一种简化各向异性矢量高斯-谢尔模型光源，该光源具有均匀、圆形、椭圆形、双曲线形及带状等五种偏振度分布形式。利用惠更斯-菲涅耳原理和矢量部分相干光束交叉谱密度矩阵理论，研究了这种光源产生的光束在自由空间传输时偏振度分布演化特性。数值计算结果表明，各向异性矢量高斯-谢尔模型光束在自由空间传输时偏振度分布具有非常复杂的演化过程，不能给出简单的演化规律。利用光源的空间相干性质，提出了偏振分布相似传输条件和远场偏振分布简化条件。当满足偏振分布相似传输条件时，光束在任意横截面的偏振度分布都和光源偏振度分布具有相似形状；当满足远场偏振分布简化条件时，偏振度分布在经过复杂演化过程后，在远场总演化成均匀或圆对称等简单分布。 2．利用扩展的惠更斯-菲涅耳原理和交叉谱密度函数理论，研究了Li-Wolf各向异性高斯-谢尔模型光束在湍流大气中传输时，自由衍射和大气湍流对光束光强分布的影响，以及在这两种影响作用下光束光强分布演化过程。根据求得的光强分布解析公式，大气湍流给光强分布带来的展宽使光强分布各向异性的程度随传输距离增加而减小，其作用随传输距离 按照 增加；通过改变光源空间相干性，自由衍射给光强分布带来的展宽使光强分布各向异性的程度随传输距离增加而增加，或随传输距离增加而减小，其作用随传输距离按照 增加。在大气湍流和自由衍射共同作用下，对确定的光源光强分布，光束的光强分布具有多种演化过程。随传输距离增加，光强分布最终都趋向圆对称分布。提出了五种减弱光源空间相干性的方式，研究了减弱光源空间相干性的不同方式对光束光强分布趋向圆对称过程的影响。当减弱光源空间相干性使光强分布 方向的均方根宽度 和 方向的均方根宽度 在远场的差异增大时，光束光强分布趋向圆对称的过程延缓；当减弱光源空间相干性使 和 在远场的差异减小时，光束光强分布趋向圆对称的过程加快。 3．提出了一种扩展的各向异性矢量高斯-谢尔模型光源，该光源也具有均匀、圆形、椭圆形、双曲线形及带状等五种偏振度分布形式。利用扩展的惠更斯-菲涅耳原理和矢量部分相干光束交叉谱密度矩阵理论，研究了这种光源产生的光束在湍流大气中传输时远场偏振度分布特性。根据求得的远场偏振度分布解析公式，具有均匀偏振度分布的光源产生的光束在远场重新获得光源处偏振度分布；具有非均匀偏振度分布的光源产生的光束在远场获得均匀偏振度分布，不能获得光源处偏振度分布，偏振度取值受光源光强分布参数影响，不受光源空间相干分布参数影响。提出了矢量高斯-谢尔模型光束在远场可重新获得光源处偏振分布的一般条件：只有当光源电场两个正交偏振分量的光强分布完全相同或只有一个常系数的差别时，矢量高斯-谢尔模型光束才可在远场重新获得光源处的偏振分布。 |
| 英文摘要 | Partially coherent beams (PCBs) are featured by small divergence angle and strong resistance to the influence of turbulent atmosphere, and are widely used in areas like laser radar and free space optical communication. Research on the propagation properties of PCBs is critical for these applications to make a reasonable choice of the beam type and source characteristic parameters. So far studies of the propagation properties of PCBs are mainly about isotropic PCBs, which have isotropic intensity distributions and isotropic spatial coherence distributions. The propagation properties of anisotropic PCBs have not been studied sufficiently until now. Real PCBs are usually anisotropic, and the existing studies cannot describe exactly the propagation properties of real PCBs, especially those beams which have anisotropic spatial coherence distributions or complex transverse polarization distributions. In this dissertation, we study the propagation properties of anisotropic PCBs with anisotropic Gaussian-Schell model beams. Specifically, we study evolution properties of the intensity distribution in turbulent atmosphere, and evolution properties of the polarization distribution in free space as well as in turbulent atmosphere. The main researches are as follows: 1. A simplified anisotropic electromagnetic Gaussian-Schell model source is proposed. It is found that, the source can have five kinds of polarization distribution patterns, including homogeneous pattern, circle-shaped pattern, ellipse-shaped pattern, hyperbolic-curve-shaped pattern, and strap-shaped pattern. By using the Huygens-Fresnel principle and the cross-spectral density matrix theory of random electromagnetic beams, the free-space propagation properties of the transverse polarization distribution of the beam generated by the source are studied. Numerical calculations show that, the evolution process of the transverse polarization distribution of the beam is quite complicated, and cannot be described by a simple evolution law. By exploiting the source correlation properties, an analogical propagation condition of the transverse polarization distribution and two far-field polarization distribution simplification conditions are put forward. When the analogical propagation condition is satisfied, the polarization distribution on an arbitrary transverse plane is analogical to that on the source plane. When one of the two far-field polarization distribution simplification conditions is satisfied, after a complex evolution process, the polarization distribution always evolves into simple patterns, i.e., homogeneous pattern or circle-shaped pattern. 2. By using the extended Huygens-Fresnel principle and the cross-spectral density theory of stochastic scalar beams, the effects of free-space diffraction and turbulent atmosphere on the transverse intensity distribution of a Li-Wolf type anisotropic Gaussian-Shell model beam propagating in turbulent atmosphere are studied. The evolution properties of the transverse intensity distribution of this kind of beams are also studied. It is found that, the effect of turbulent atmosphere tends to decrease the anisotropy of the intensity distribution, and its effect increases with distance according to . On the other hand, by varying the source coherence, the effect of free-space diffraction can decrease or increase the anisotropy of the intensity distribution, and its effect increases with distance according to . Under the influence of both the turbulent atmosphere and the free-space diffraction, for a given source intensity distribution, the beam intensity distribution can have many different evolution processes. As the propagation distance grows continuously, the intensity distribution always tends to a circular shape in the far field. Five kinds of ways to deteriorate the source spatial coherence are proposed. The effect of deteriorating the source coherence on the distance needed by the beam intensity distribution to tend to a circular shape is studied. It is found that, as the source coherence is worsened differently, the process of the beam intensity distribution tending to a circular shape is affected differently. When deteriorating the source coherence makes the far-field difference between the rms widths and of the beam intensity distribution become larger, it slows down the process of the beam intensity distribution tending to a circular shape. Otherwise, when deteriorating the source coherence makes this difference become smaller, it accelerates the process of the beam intensity distribution tending to a circular shape. 3. An extended anisotropic electromagnetic Gaussian-Schell model source is proposed. It is found that, the source can also have five kinds of polarization distribution patterns, including homogeneous pattern, circle-shaped pattern, ellipse-shaped pattern, hyperbolic-curve-shaped pattern, and strap-shaped pattern. By using the extended Huygens-Fresnel principle and the cross-spectral density matrix theory of random electromagnetic beams, the far-field transverse polarization distribution properties are studied when the beam generated by the source propagates in turbulent atmosphere. The research results show that, the beam which has homogeneous polarization distribution on the source plane will regain the source polarization distribution in the far field. Otherwise, the beam which has inhomogeneous polarization distribution on the source plane will have homogeneous polarization distribution in the far field, and the far-field degree of polarization is affected by the source intensity characteristic parameters, and not affected by the source spatial coherence characteristic parameters. Based on a complete knowledge of the far-field polarization distribution properties of electromagnetic Gaussian- Schell model beams in turbulent atmosphere, a general source-plane polarization distribution reconstruction condition is given. This condition shows that, electromagnetic Gaussian-Schell model beams can regain their source polarization distributions in the far field if the two intensity distributions corresponding to the two orthogonal polarization components of the source electric field are the same, or if they differ only by a constant proportionality coefficient. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15720]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 张荣. 各向异性部分相干光束空间传输特性研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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