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。     

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 partially coherent double-vortex beams in turbulent atmosphere

Based on the extended Huygens–Fresnel principle, we study the propagation properties of partially coherent double-vortex beams in turbulent atmosphere. The intensity distribution of the beams on propagation and the influence of the characteristic parameters are investigated in great detail. It is shown that when the beams propagate in turbulent atmosphere, the intensity distributions are of double-ring structure near the source plane, but they will experience change, which are determined by the topological charges, the spatial coherence, source beam width and atmospheric turbulence. These results may have applications in space optical communication.     

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.     

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.     

Changes in the spectrum and polarization of polychromatic partially coherent electromagnetic beams in the turbulent atmosphere

The polychromatic partially coherent electromagnetic Cosh-Gaussian (EChG) beam is introduced and taken as a typical example of polychromatic partially coherent electromagnetic beams. Based on the unified theory of coherence and polarization, the expressions for the spectrum and the degree of polarization of polychromatic partially coherent EChG beams in the turbulent atmosphere are derived, and the conditions for keeping polarization invariance and for determining the position where the degree of polarization becomes zero along the propagation path are also given. It is shown that the normalized spectrum is close to the normalized source spectrum due to turbulence. The reasonable physical explanation of spectral shift is given. On the other hand, the bandwidth does not affect the degree of polarization, and the degree of polarization tends to the value at the source plane due to turbulence in the long-propagation distance limit. The spectrum and polarization of polychromatic electromagnetic Gaussian Schell-model (EGSM) beams and electromagnetic Gaussian (EG) beams in turbulence are treated as special cases of polychromatic partially coherent EChG beams.     

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     

部分相干空心光束在湍流介质中的传输特性

根据广义的惠更斯-菲涅耳原理，得到了相干度为零阶贝塞耳函数的部分相干空心光束在湍流介质中传输特性的理论公式.据此研究了这种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源光斑大小均会影响光束的传输特性.     

Polarization changes in partially coherent electromagnetic beams propagating through turbulent atmosphere

Abstract

In this paper, we study the effects of turbulent atmosphere on the degree of polarization of a partially coherent electromagnetic beam, which propagates through it. The beam is described by a 2?2 cross–spectral density matrix and is assumed to be generated by a planar, secondary, electromagnetic Gaussian Schell–model source. The analysis is based on a recently formulated unified theory of coherence and polarization and on the extended Huygens–Fresnel principle. We study the behaviour of the degree of polarization in the intermediate zone, i.e. in the region of space where coherence properties of the beam and the atmospheric turbulence are competing. We illustrate the analysis by numerical examples.     

Polarization changes in partially coherent electromagnetic beams propagating through turbulent atmosphere

In this paper, we study the effects of turbulent atmosphere on the degree of polarization of a partially coherent electromagnetic beam, which propagates through it. The beam is described by a 2⊗2 cross-spectral density matrix and is assumed to be generated by a planar, secondary, electromagnetic Gaussian Schell-model source. The analysis is based on a recently formulated unified theory of coherence and polarization and on the extended Huygens-Fresnel principle. We study the behaviour of the degree of polarization in the intermediate zone, i.e. in the region of space where coherence properties of the beam and the atmospheric turbulence are competing. We illustrate the analysis by numerical examples.     

Changes of propagation characteristic parameters for partially coherent Hermite-Gaussian beams in a turbulent atmosphere

Based on the extended Huygens-Fresnel principle and the definition of second-order moments of the Wigner distribution function (WDF), the analytical formulas for the root-mean-square (rms) spatial and angular widths and the M²-factor of partially coherent Hermite-Gaussian (PCHG) beams propagating through atmospheric turbulence are derived. The major factors affecting on the M²-factor are also discussed in detail. The results show that the rms spatial and angular widths and the M²-factor increase with the propagation distance and the strength of turbulence. However, the relative rms spatial and angular widths and the relative M²-factor of PCHG beams with a higher order, lower coherence and longer wavelength are less affected by the turbulence.     

Effective Rayleigh range of partially coherent beams propagating through the turbulent atmosphere

The concept of the Rayleigh range of partially coherent beams is extended from free space to the turbulent atmosphere. The general analytical expression for the effective Rayleigh range of partially coherent beams propagating through the turbulent atmosphere is derived. It is shown that the longer the free-space Rayleigh range is, the more the effective Rayleigh range is affected by turbulence, which is illustrated by numerical calculation examples.     

Propagation properties of radial partially coherent flat-topped array beams in a turbulent atmosphere

With the help of the tensor method, the analytical expression for the cross-spectral density of the radial partially coherent flat-topped array (RPCFTA) beams propagating in a turbulent atmosphere is derived, where the correlated superposition and uncorrelated superposition are considered. The average intensity, the spatial coherence properties and power in bucket (PIB) of these kinds of beams are investigated in detail. It is shown by numerical results and analysis that the average intensity and the spatial coherence of the correlated or uncorrelated RPCFTA beams will change on propagation and this change is dependent upon the correlation of the source's beamlets and atmospheric turbulence. In addition, the comparisons of the average intensity and the spatial coherence between the correlated and the uncorrelated RPCFTA beams propagating both in turbulent atmosphere and in free space are also given, and some interesting results are obtained. The laser power of focus ability of the single PCFT beam is worse than that of the correlated RPCFTA beam and but better than that of the uncorrelated RPCFTA beam when propagation distance in turbulent atmosphere is far-field plane.     

Spatial correlation properties of apertured partially coherent radially polarized beams in turbulent atmosphere

Based on the extended Huygens–Fresnel integral, the analytical formulae for the cross-spectral density matrix of the partially coherent radially polarized beams diffracted at a circular aperture in turbulent atmosphere are derived. The unapertured and free-space cases can be viewed as the special cases of our general result. By using the degree of coherence formula, the spatial correlation properties of the apertured partially coherent radially polarized beams in turbulent atmosphere are studied. The analyses indicate that the spatial correlation of the apertured partially coherent radially polarized beams are more affected by the atmospheric turbulence with the larger structure constant, the smaller truncation parameter, the larger coherence length, and the farther propagation distance.     

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 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 partially coherent partially phase-locked laser array in turbulent atmosphere

The mechanism for beam quality degradation in recently developed phase locking of high power solid state lasers, which is caused mainly by partially coherent property of element beam and partially phase locking of the laser array, is analyzed in detail. Analytical expression for propagation of partially coherent partially phase-locked laser array in turbulent atmosphere is obtained based on extended Huygens-Fresnel principle. The effect of coherence width, phase error and intensity of turbulence on the beam quality in the target-plane is studied in detail. The tolerance on phase error for laser array with different coherence property is analyzed. It is concluded that the laser array with better coherence is more sensitive to turbulence, and phase control can improve beam quality in the receiving plane only in the case when the element beam has good beam quality and propagates in weak turbulence.