部分相干涡旋光束在湍流大气中的传输特性

根据广义的惠更斯-菲涅耳原理,推导了部分相干涡旋光束在湍流介质中传输时光强分布情况的理论公式,详细研究了部分相干涡旋光束在湍流介质中的传输变化规律。研究结果表明,湍流介质的强弱,光源的相干性以及光束所带拓扑电荷数大小均会影响光束传输特性。     

部分相干光束经过湍流大气传输研究进展

相较于相干光束,部分相干光束经过湍流大气传输能够有效地抑制湍流引起的光束展宽、光斑漂移及光强闪烁等扰动效应,在自由空间光通信、激光雷达和激光遥感等方面有重要的应用前景.近年来,部分相干光束湍流大气传输研究受到越来越多学者的关注.本文回顾了部分相干光束在湍流大气中传输特性研究的发展历程、理论基础及常用的理论方法,介绍了处理光束经过湍流大气传输的相位屏数值模拟方法,以及如何把该方法运用到处理部分相干光束传输.     

部分相干平顶光束在梯度折射率介质中的传输特性

利用广义惠更斯-菲涅尔衍射积分方法,推导出部分相干平顶光束在梯度折射率介质中传输的交叉谱密度函数解析表达式,对部分相干平顶光束在梯度折射率介质中的传输特性进行了分析,并进一步讨论了介质梯度折射率系数、光束阶数以及光束相干性对传输特性的影响.结果表明,部分相干平顶光束在梯度折射率介质中传输时的轴上光强分布呈现周期性变化了,且周期由梯度折射率系数决定,而与光束相干性无关.光束阶数越高、相干性越好、介质梯度折射率系数越大,则在介质中的轴上峰值光强越大.并且,在光强峰值位置附近的光强分布随传输距离的变化非常剧烈.     

部分相干电磁光束在湍流介质中传输的偏振变化

从推广的惠更斯-菲涅尔原理出发,推导出了部分相干电磁光束的偏振态在湍流介质中传输的表达式。并以电磁高斯-谢尔模型(EGSM)光束为例,研究了湍流对电磁高斯-谢尔模型光束偏振态的影响。研究结果表明,对于轴上点,湍流介质的折射率结构常数越大,偏振度趋于最大值的速度越快,达到的最大值越小;光斑越大,偏振度达到最大值的位置离光源越远,在光斑增大的过程中,偏振度所达到的极大值会先增大后减小,最后保持与光源相同的偏振度不变。对于轴外点,一个固定的z,光的偏振度随着离轴距离的增大而逐渐下降,并最终等于零。折射率结构常数越大,偏振度随离轴距离的增大而下降得越缓慢;光斑越大,偏振度随离轴距离的增大下降得越快。     

部分相干电磁光束在湍流介质中传输的偏振变化

 从推广的惠更斯-菲涅尔原理出发,推导出了部分相干电磁光束的偏振态在湍流介质中传输的表达式。并以电磁高斯-谢尔模型(EGSM)光束为例,研究了湍流对电磁高斯-谢尔模型光束偏振态的影响。研究结果表明,对于轴上点,湍流介质的折射率结构常数越大,偏振度趋于最大值的速度越快,达到的最大值越小;光斑越大,偏振度达到最大值的位置离光源越远,在光斑增大的过程中,偏振度所达到的极大值会先增大后减小,最后保持与光源相同的偏振度不变。对于轴外点,一个固定的z,光的偏振度随着离轴距离的增大而逐渐下降,并最终等于零。折射率结构常数越大,偏振度随离轴距离的增大而下降得越缓慢;光斑越大,偏振度随离轴距离的增大下降得越快。     

非均匀部分相干光束在自由空间中的传输

本文介绍了非均匀部分相干光束的概念, 并用数值模拟的方法详细研究了其在自由空间传输后的变化. 研究结果表明, 经过自由空间传输后非均匀部分相干光束会发生不同于传统相干模型光束的显著变化. 这种变化和光束传输距离、光源空间相干度分布、光源光强分布密切相关. 经过传输后, 源平面自相干附近点的空间相干度发生突变, 在短距离传输过程中源平面高相干区域的空间相干度会降低, 接收面各点的空间相干曲线不再相同, 随着传输距离增加, 非均匀空间相干度会逐渐趋于均匀.     

超常介质中部分相干光束传输的调制不稳定性研究

超常介质与常规光学介质的一个最重要的区别是前者具有色散磁导率,其折射率呈现出可正可负,这样调制不稳定性出现新特点。借助于Wigner变换,从一般的非线性薛定谔方程出发,得到了部分相干光满足Wigner-Moyal的方程,获得了色散关系和增益谱,揭示了部分相干度不仅可抑制调制不稳定性,而且还可以缩小发生不稳定性的频率范围。     

高斯型非均匀部分相干光的大气湍流传输特性

基于广义惠更斯-菲涅耳原理和交叉谱密度函数,对高斯型非均匀关联的部分相干光束在大气湍流中的传输特性进行了研究.结果表明,部分相干光的相干度的变化和源平面的高斯调制半宽、传输距离等有着密切关系.在传输过程中,初始平面相干度分布存在突变,在传输过程中消失;光束中两点的相干度随着传输距离的增加先增大后减小,并且相干度的分布由非均匀分布变成均匀分布.这种非均匀关联的部分相干光束在激光通信领域具有广阔的应用前景.     

部分相干涡旋光束在大气湍流中的远场传输特性

运用广义惠更斯-菲涅耳原理,详细研究了部分相干涡旋光束在湍流介质中的远场传输规律.研究表明,部分相干涡旋光束的光谱相干度及光强分布与光束的拓扑电荷数、空间相对相干长度及湍流介质的折射率结构常数等因素有关.在湍流介质中,光谱相干度存在相位奇点,并且随着空间相对相干长度的增大,相干涡旋逐渐演化为强度涡旋,而湍流介质的强弱对部分相干涡旋光束的影响则相反,随着湍流介质的折射率常数的增大,强度涡旋逐渐演化为相干涡旋.     

多色部分相干偏心光束在non-Kolmogorov湍流中的传输

推导了多色部分相干偏心光束在non-Kolmogorov 湍流中传输的总光强、轴上光谱、相干度的解析表达式, 研究了光束偏心参数β 、湍流广义指数α和源光谱带宽Ω对激光传输特性的影响. 研究表明: β越大, 则光束重心偏离传输轴越远, 相干度的不对称性越明显, 但是, β对轴上光谱几乎没有影响; 湍流广义指数α对总光强、 轴上光谱和相干长度的影响是非单调的, 当α=3.1时, 湍流对光束传输特性的影响最大. 值得指出的是: 在某些传输距离处, 不同α对应的轴上光谱位移量相同; 在某些传输距离处, 轴上光谱位移量为零, 且该传输距离与Ω无关, 但湍流使得该传输距离缩短. 所得结论对多色部分相干偏心光束在 湍流大气中传输的相关应用具有重要意义. 关键词： non-Kolmogorov湍流 多色部分相干偏心光束 光谱强度 相干度     

Propagation of partially coherent Bessel-Gaussian beams in turbulent atmosphere

The characteristics of partially coherent Bessel-Gaussian beams propagating in turbulent atmosphere are investigated. Based on the extended Huygens–Fresnel principle, the influence of topological charges and coherence of the source on the intensity and the degree of coherence in the received plane are considered. The influence of atmospheric turbulence on beam profile and coherence in the received plane is also analyzed. It is found that a Bessel-Gaussian shaped intensity distribution will eventually transform into a Gaussian distribution after propagating in turbulent atmosphere. Meanwhile, topological charges, coherence of the source and atmospheric turbulence will also influence the propagation characterizations of the beams.     

Propagation of Gauss--Bessel beams in turbulent atmosphere

This paper studies the propagation properties of Gauss--Bessel beams in a turbulent atmosphere. Based on the extended Huygens--Fresnel principle, it derives the intensity distribution expression for such beams propagating in a turbulent atmosphere. Then the influence of turbulence and source beam parameters on the beam propagation is studied in great detail. It finds that the intensity distribution of Gauss--Bessel beams will change into Gaussian profile in a turbulent atmosphere, and that stronger turbulence and smaller topological charges will lead to a faster changing.     

Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained.It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.     

Propagation properties of partially coherent Laguerre-Gaussian beams in turbulent atmosphere

To study the propagation properties of partially coherent Laguerre-Gaussian (PLG) beams through turbulent atmosphere, the analytical formulas are derived for the angular width and the beam-propagation factor (M²-factor) of PLG beams by using the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function (WDF). The corresponding numerical results are also calculated. When propagation distance increases, the angular width is found to spread faster for PLG beams with higher beam order, smaller correlation length and bigger structure constant The angular width of PLG beams decreases with increase in waist width (w₀).The M²-factor of PLG beams with higher beam order and smaller correlation length is less affected by turbulence with increase in propagation distance. The propagation properties of the M²-factor for PLG beams with the smaller structure constant are better than that with bigger structure constant . The M²-factor of PLG beams decreases with increase in the wavelength λ, and it is also less affected by turbulence for beams with higher order and smaller correlation length. Furthermore, for the PLG beams with the same beam order, the angular width and the M²-factor keep invariable in free space.     

Propagation of partially coherent controllable dark hollow beams with various symmetries in turbulent atmosphere

Normalized intensity distribution, the complex degree of coherence and power in the bucket for partially coherent controllable dark hollow beams (DHBs) with various symmetries propagating in atmospheric turbulence are derived using tensor method and investigated in detail. Analytical results show that, after sufficient propagation distance, partially coherent DHBs with various symmetries eventually become circular Gaussian beam (without dark hollow) in turbulent atmosphere, which is different from its propagation properties in free space. The partially coherent DHBs return to a circular Gaussian beam rapidly for stronger turbulence, higher coherence, lower beam order, smaller p or smaller beam waist width. Another interesting observation is that the profile of the complex degree of coherence attains a similar profile to that of the average intensity of the related beam propagating in a turbulent atmosphere. Besides the laser power focusablity of DHBs are better than that of Gaussian beam propagating in turbulent atmosphere.     

Propagation of cylindrical vector beams in a turbulent atmosphere

<正>Based on the extended Huygens-Presnel principle,the propagation of cylindrical vector beams in a turbulent atmosphere is investigated.The intensity distribution and the polarization degree of beams on propagation are studied. It is found that the beam profile has a Gaussian shape under the influence of the atmospheric turbulence,and the polarization distribution shows a dip in the cross section as the beam propagates in the turbulent atmosphere.It is also found that the beam profile and the polarization distribution are closely related to beam parameter and atmospheric turbulence.     

Propagation properties of stochastic electromagnetic double-vortex beams in turbulent atmosphere

Based on the extended Huygens-Fresnel principle, we study the propagation properties of stochastic electromagnetic double-vortex beams in turbulent atmosphere. The result shows that the spreading of the partially coherent double-vortex beams can be smaller than that of the fully coherent ones. The degree of polarization of this kind of beam will experience change, which is dependent on the degree of polarization of the source plane, the atmospheric turbulence, topological charge, and the spatial coherence. The results may have applications in space optical communication.     

部分相干双曲余弦高斯光束通过湍流大气的光束扩展

基于广义惠更斯-菲涅尔原理，并采用将部分相干双曲余弦高斯光束用厄米-高斯光束的非相干叠加表示的方法，研究了部分相干双曲余弦高斯光束通过湍流大气的光束扩展问题，推导出了部分相干双曲余弦高斯光束通过湍流大气均方根束宽的解析表达式.研究表明，部分相干双曲余弦高斯光束的扩展随着湍流大气的折射率结构常数C²_n和光束离心参数δ的增大而加剧.但是，随着δ的增大，部分相干双曲余弦高斯光束受到湍流的影响减小. 关键词： 部分相干双曲余弦高斯光束 湍流大气 光束扩展