部分相干光在大气湍流中的到达角起伏

研究了部分相干高斯谢尔光束在大气湍流中的到达角起伏.主要采用湍流内外尺度的修正Von Karmon谱模型及广义惠更斯-菲涅尔原理和交叉谱密度函数推导出了部分相干光在大气湍流中的到达角起伏表达式.对比分析了湍流内外尺度、湍流强度、传输距离、源相干参数以及波长等参数对部分相干光在大气湍流水平路径上传输时的到达角起伏的影响.结果表明:随着传输距离的增加,到达角起伏越来越小;随着大气湍流内外尺度和源相干参数的增加,到达角起伏也越来越大;与部分相干光相比,完全相干光的到达角起伏受湍流影响很小;随着波长和湍流强度的减小,到达角起伏越来越小.     

湍流对椭圆偏振激光传输中偏振特性的影响分析EI北大核心CSCD

根据推广的惠更斯-菲涅耳原理和Rytov相位结构函数二次近似,推导出高斯-谢尔模型光束在湍流大气传输中交叉谱密度矩阵的表达式,研究了湍流对椭圆偏振高斯-谢尔模型光束传输中的偏振特性影响,并与部分偏振高斯-谢尔模型光束进行了对比分析.结果表明,相对于部分偏振高斯-谢尔模型光束,椭圆偏振高斯-谢尔模型光束在湍流大气传输中偏振度、方位角以及椭圆度的变化受湍流的影响较小.同时得到椭圆偏振高斯-谢尔模型光束在湍流大气斜程传输中偏振度的变化幅度比部分偏振高斯-谢尔模型光束的小,而方位角和椭圆度的变化幅度比部分偏振高斯-谢尔模型光束的大.     

大气湍流对部分相干厄米-高斯光束空间相干性的影响

基于广义惠更斯-菲涅耳原理,并采用Rytov相位结构函数二次近似,推导出了部分相干厄米-高斯(H-G)光束通过大气湍流传输的光谱相干度公式,研究了湍流对光束的空间相干特性的影响.研究表明,部分相干H-G光束通过大气湍流传输其光谱相干度会出现振荡和相位奇异现象,但随着湍流的增强,振荡减弱,直至振荡和相位奇异现象消失,这一特性与高斯-谢尔模型光束的差异很大.光束的相干参数越小,光束空间相干性受湍流的影响也越小.此外,还研究了光谱相干度二阶矩宽度与光谱强度二阶矩宽度间的关系,得到一些有意义的结果,并给出了合理的 关键词： 部分相干厄米-高斯光束 大气湍流 光谱相干度 二阶矩宽度     

大气湍流对部分相干电磁平顶光束传输的影响

基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯-谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顶光束的光谱跃变现象消失.     

大气湍流对部分相干电磁平顶光束传输的影响

基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯一谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顸光束的光谱跃变现象消失.     

非均匀拉盖尔-高斯关联光束及其传输特性

提出了一种新型特殊关联部分相干光束即非均匀拉盖尔-高斯关联光束,其在x和y方向上的关联结构函数分别为非均匀关联和拉盖尔-高斯关联函数.基于广义惠更斯-菲涅耳衍射积分公式,推导了这种光束交叉谱密度函数在自由空间以及大气湍流中的传输式,并计算了该光束经过自由空间和湍流大气传输的光强分布和关联结构函数分布演化特性.研究发现,该光束光强分布在传输过程中展现出自聚焦、自偏移和自分裂等奇异特性,同时发现控制关联结构函数参数可以有效地降低湍流大气的影响.关联结构调控为操控光束传输行为提供了一种新颖而有效的手段,在大气激光通信、微粒操控等领域具有重要的应用前景.     

大气湍流中部分相干聚焦涡旋光束的传输特性

基于广义惠更斯-菲涅耳原理和相位结构函数的平方近似,研究了部分相干高斯-谢尔模型涡旋光束被聚焦后在大气湍流中的传输特性,得到了焦平面上光强解析表达式.利用该表达式,详细研究了该类光束在大气湍流中传输焦平面上的光强分布特性.结果表明：在大气湍流中,随着传输距离的增加,涡旋光束的奇异性逐渐降低.对于拓扑荷大的以及空间相干长度较长的涡旋光束,光束奇异性的保持相对要好.在一定的焦距长度和湍流大气条件下,我们可以通过调整光源的拓扑荷和相干长度控制焦面光强分布和焦斑大小.另外,有一定拓扑荷的涡旋光束可以在一定程度上降低大气湍流对传输光束焦面光强分布的影响.     

大气湍流对斜程传输准单色高斯-谢尔光束时间相干性的影响

由第一类零阶贝塞尔函数的级数展开推导出波结构函数在任意湍流条件下的近似表达式。由广义惠更斯-菲涅耳原理、随高度变化的Hufnagel-Valley湍流廓线模型以及波结构函数在任意湍流条件下的近似表达式,导出了斜程传输时准单色高斯-谢尔光束互相干函数的解析式。然后,利用表征光束时间相干性的纵向相干长度(可由互相干函数导出),研究了斜程传输时大气湍流对准单色高斯-谢尔光束时间相干性的影响。研究结果表明,准单色高斯-谢尔光束的时间相干性在整个斜程传输过程中保持不变。最后,对该结果在物理上给予了定性解释。     

大气湍流对多色高斯-谢尔模型光束扩展的影响

基于广义惠更斯-菲涅耳原理,采用Rytov相位结构函数二次近似和硬边窗口函数的复高斯展开法,推导了受光阑限制的多色高斯-谢尔模型(GSM)光束在大气湍流中的二阶矩束宽公式。研究表明:二阶矩束宽随着大气湍流折射率结构常数、源光谱带宽和光束传输距离的增加而增大,随着光束截断参数和光束相干参数的增加而减小;并且,当源光谱带宽越大、光束截断参数和光束相干参数越小,则湍流对受光阑限制的多色GSM光束扩展的影响就越小。关键词:      

部分相干涡旋光束通过大气湍流上行和下行传输的比较研究

基于广义惠更斯-菲涅耳原理,以高斯-谢尔模型(GSM)涡旋光束作为典型的部分相干涡旋光束,推导出GSM涡旋光束通过大气湍流斜程传输的平均光强、均方根束宽和交叉谱密度函数的解析表达式,并用以研究了大气湍流中上行和下行对GSM涡旋光束传输和对相干涡旋的影响.结果表明,在相同条件下,GSM涡旋光束下行传输受大气湍流的影响要小于上行传输,下行传输时相干涡旋拓扑电荷守恒距离要长于上行传输.对所得结果做了物理解释. 关键词： 部分相干涡旋光束 相干涡旋 大气湍流 上行和下行传输     

Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence

On the basis of the extended Huygens-Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector,the characteristics of the partially coherent Gaussian Schell-model(GSM) beams propagating in slanted atmospheric turbulence are studied.Using the cross-spectral density function(CSDF),we derive the expressions for the effective beam radius,the spreading angle,and the average intensity.The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically.The influences of the coherence degree,the propagation distance,the propagation height,and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.     

Study on the spatial coherence of vortex Gaussian beams passed atmospheric turbulence

In this paper, the spectral degree of coherence formula was derived by using the generalized Huygens–Fresnel principle and the method of Rytov phase structure function quadratic approximation. The spatial coherence of vortex Gaussian beams passed atmospheric turbulence was studied. It showed that the spatial coherence was mainly affected by the coherence of light source, the number of topological charges and the transmission distance. The distance of transmission was farther, the spatial coherence of beam was better. The number of topological charges were more, the spatial coherence of beam was better. In a certain transmission distance, the coherence of light source was better, the spatial coherence of beam was worse. In addition, there were coherent vortexes which spectral degree of coherence was zero after the partially coherent vortex beams getting through atmospheric turbulence transmission.     

Propagation Characteristics of a Partially Coherent Gaussian Schell-model Array Vortex Beam in the Joint Turbulence Effect of a Jet Engine and Atmosphere

This work investigates the joint effects of jet engine exhaust-induced turbulence and atmospheric turbulence on the propagation of a partially coherent Gaussian Schell-model Array (GSMA) vortex beam. Using the two-process propagation method, analytical formulae are derived for the cross-spectral density, spectral density, degree of coherence, and beam width of the considered beam. The results show that the considered beam takes different shapes; when the spatial coherence is large, the spectral density of the GSMA vortex beam takes an elliptical shape, whereas when the spatial coherence is smaller, the spectral density remains a Gaussian shape. The evolution profile of the degree of coherence weakens gradually when the propagation distance, topological charge, and turbulence strength increase. Moreover, the profile of the degree of coherence takes the Gaussian profile when the propagation distance is longer or turbulence atmospheric is stronger. Furthermore, the results reveal that the corresponding beam spreads faster with a larger propagation distance, lower spatial coherence, and high-strength turbulence. This study also concludes from the results that the beam is affected more when its propagation is near the jet engine exhaust, which means that this latter has a significant impact.     

高斯谢尔光束通过湍流大气漫射目标的散射统计

基于广义惠更斯菲涅耳原理分析了高斯谢尔光束通过湍流大气漫射目标的散射统计特性。假定相位结构函数起主导作用,根据高斯谢尔光束的交叉密度函数,推导了散斑场的互相干函数表达式,进而得出接收面处的散斑尺寸大小和强湍流起伏的时延协方差函数表达式。数值分析了源相干长度、波长、湍流强度对互相干函数的影响。对理想漫射目标,接收面的散斑尺寸大小由束腰宽度、源相干长度和湍流强度确定,随着湍流强度的增加,散斑尺寸变小;在弱湍流区,散斑尺寸由源相干长度决定,当湍流增强时,散斑尺寸大小逐渐趋于一致。     

Change in degree of coherence of partially coherent electromagnetic beams propagating through atmospheric turbulence

We study the change in the degree of coherence of partially coherent electromagnetic beam (so called electromagnetic Gaussian Schell-model beam). It is shown analytically that with a fixed set of source parameters and under a particular atmospheric turbulence model, an electromagnetic Gaussian Schell-model beam propagating through atmospheric turbulence reaches its maximum value of coherence after the beam propagates a particular distance, and the effective width of the spectral degree of coherence also has its maximum value. This phenomenon is independent of the used turbulence model. The results are illustrated by numerical curves.     

The far-field spatial coherence of Gaussian Schell-model beam in turbulence in terms of position vectors

Spatial coherence properties of beam produced by Gaussian Schell-model source when the beam is propagating through atmosphere have been analyzed in terms of position vectors. New expressions for cross-spectral density of optical field and spectral degree of coherence as well as radiant intensity have been developed. Numerical results illustrated in this paper indicate the coherence degradation suffered from atmospheric turbulence and their directional dependence.     

Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence

Atmospheric turbulence causes strong irradiance fluctuations of propagating optical wave under the severe weather conditions in long-distance free space optical communication. In this paper, the scintillation index for a Gaussian beam wave propagation through non-Kolmogorov turbulent atmosphere is derived in strong fluctuation regime, using non-Kolmogorov spectrum with a generalized power law exponent and the extended Rytov theory with a modified spatial filter function. The analytic expressions are obtained and then used to analyze the effect of power law, refractive-index structure parameter, propagation distance, phase radius of curvature, beam width and wavelength on scintillation index of Gaussian beam under the strong atmospheric turbulence. It shows that, with the increasing of structure parameter or propagation distance, scintillation index increases sharply up to the peak point and then decreases gradually toward unity at rates depending on power law. And there exist optimal value of radius of curvature and beam width for minimizing the value of scintillation index and long wavelength for mitigating the effect of non-Kolmogorov strong turbulence on link performance.     

根据到达角协方差测量大气湍流外尺度

通过湍流大气中光波相位结构函数得到两点间的到达角协方差与大气湍流外尺度的关系,并利用差分到达角方差进行了归一化,进而得到大气湍流外尺度和差分到达角方差及到达角协方差的表达式。采用四孔到达角起伏测量仪进行了近地面水平路径的实验,测量结果表明在离地面6 m的高度上,湍流外尺度在4 m左右,并随时间变化,不同方向的测量结果有一些差别。