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题名	部分相干光束空间传输特性的研究
作者	王华
学位类别	博士
答辩日期	2008
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 大气湍流 时间相干性 空间相干性 偏振态
其他题名	Research on the propagation of partially coherent electromagnetic beams in space
中文摘要	部分相干光束是一种空间相干性较差的光束，但是它仍具有方向性好的优点。由于其空间相干性差，所以较完全相干的激光光束受大气湍流的影响小。由于这上述两优点，部分相干光束很有希望取代激光光束应用于激光空间通讯、激光雷达和激光遥感等领域。然而，目前对部分相干光束空间传输特性的研究，均针对单色与各向同性光束。实际的光束即不是严格的单色光束也不是严格的各向同性光束，所以需要研究准单色光束与各向异性光束的空间传输特性。另外，在实际应用中，光束通常是斜程传输的，因此需要考虑大气湍流强度随海拔高度变化的情况。本论文正是在上述三个方向做了一定的探索： 1、基于广义Huygens－Fresnel原理与大气湍流的Kolmogorov谱模型，首次研究了大气湍流对水平传输准单色部分相干光束时间相干性与空间相干性的影响。研究结果表明：①、在传输过程中准单色部分相干光束的时间相干性保持不变。②、准单色部分相干光束的空间相干性先增强，达到一个最大值后开始下降，并持续下降。③、空间相干性不同的多种准单色部分相干光束在湍流大气中传输一定距离后空间相干性趋于相同。 2、基于广义Huygens－Fresnel原理与大气湍流的Hufnagel－Valley湍流廓线模型，首次研究了大气湍流对斜程传输准单色部分相干光束时间相干性与空间相干性的影响。研究结果表明：①、与水平传输相同，在斜程传输过程中准单色部分相干光束的时间相干性仍保持不变。②、当 时（θ为天顶角，即传输路径与竖直方向的夹角），准单色部分相干光束空间相干性随传输距离均为先迅速增强，后缓慢增强，最后基本保持不变。③、当 时，准单色部分相干光束空间相干性随传输距离均为先增强，达到一个最大值后开始下降并持续减小。 3、基于Huygens－Fresnel原理、矢量光场相干与偏振统一理论和各项异性部分相干光束交叉谱密度矩阵的张量表述，首次研究了空间相干性与光源光强分布各向异性对各项异性部分相干光束自由空间传输特性的影响。研究结果表明：①、各向异性部分相干光束的空间相干性对其自由空间传输特性有很强的影响。由于空间相干性不同，即使在光源平面处两束光的光强分布与谱偏振态完全相同，但是仅传输较短距离后（例如50米），两束光的光强分布和谱偏振态已有明显差别。②、光源光强分布各向异性对各向异性部分相干光束偏振度有较强的影响。当光源光强分布各向异性时，无论对于完全偏振光束还是部分偏振光束（光束的空间相干性相同），它们在自由空间中传输一段距离（例如200米）后光束的谱偏振度都将发生明显改变。此外，光强分布各向异性的程度越大，对光束偏振度的影响也越大。
英文摘要	Partially coherent electromagnetic(PCE) beams are a kind of beams with low spatial coherence, but they are highly directional beams. These beams are less sensitive to the effects of atmospheric turbulence than fully coherent ones. They are promising beams to replace laser beams in areas of space laser communications, laser radar, laser remote sensing and so on. However, to our knowledge, the propagation of quasi-monochromatic PCE beams and anisotropy PCE beams has not been investigated up to now. In this thesis, we study the propagation. First, based on the extended Huygens–Fresnel principle and the Kolmogorov theory of turbulence, an analytical formula for the mutual coherence function of quasi-monochromatic PCE beams propagating through turbulent atmosphere is derived. Then the influence of atmospheric turbulence on the spatial and the temporal coherence is studied by employing the lateral coherence length and the longitudinal coherence length to characterize the spatial coherence and the temporal coherence, respectively. It has been found that the lateral coherence length increases firstly and reaches a maximum value, and then decreases as the beam propagates in a turbulent atmosphere. On the other hand, the longitudinal coherence length remains unchanging in this propagation. Beams with different lateral coherence lengths at the source plane will have almost the same lateral coherence length as they propagate a certain distance in the turbulent atmosphere. Second, based on the extended Huygens-Fresnel principle, the Hufnagel-Valley profile model of the turbulence which is dependent on altitude, and the wave structure function under all conditions of atmospheric turbulence, the mutual coherence function of quasi-monochromatic PCE beams propagating in the slant path through the turbulent atmosphere is derived analytically. The effect of atmospheric turbulence on the temporal coherence and the spatial coherence of those beams is studied. The results show that: ①, The temporal coherence keeps unchanging in the propagation. ②, If (θis the zenith angle), the lateral coherence length increases firstly and then keeps unchanging as the beam propagates in the turbulent atmosphere. ③, If , the lateral coherence length increases firstly and then reaches its maximum value as the beam propagates a certain distance in the turbulent atmosphere, then it begins degrading and keeps decreasing with increasing distance. 088θ≤089θ≥ Third, based on the extended Huygens-Fresnel principle, the tensor representation of the cross-spectral density matrix and the unified theory of coherence and polarization of random electromagnetic beams, the propagation of anisotropic PCE beams in free space is studied. The results show that: ①, Anisotropic stochastic electromagnetic beams that propagate from the source plane z=0 into the half-space z>0 may have different beam shapes (i.e.,spectral density) and states of polarization in the half-space, even though they have the same beam shape and states of polarization in the source plane. This fact is due to a difference in the coherence properties of the field in the source plane. ②, Different stochastic electromagnetic beams generated by the sources with the same coherence properties propagating from the plane z = 0 into the half-space z > 0 will have different spectral degrees of polarization in the half-space. This fact is due to a possible difference in the anisotropy of the field in the source plane. Furthermore, the larger the anisotropy of the field in the source plane is, the larger the degree of polarization of stochastic electromagnetic beams on propagation changes.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15232]
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	王华. 部分相干光束空间传输特性的研究[D]. 中国科学院上海光学精密机械研究所. 2008.

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