高斯-谢尔模型列阵光束的远场发散角和远场辐射强度

推导出了高斯-谢尔模型（GSM）列阵光束通过自由空间传输其二阶矩束宽、远场发散角和远场辐射强度的解析表达式,并给出了GSM列阵光束与高斯光束具有相同远场发散角的条件.研究表明,具有相同远场发散角的GSM列阵光束与对应的高斯光束并不具有相同的远场辐射强度分布,这一特性与单束GSM光束的差异很大. 关键词： 高斯-谢尔模型列阵光束 远场发散角 远场辐射强度     

大气湍流对径向分布高斯列阵光束扩展和方向性的影响

采用积分变换的技巧,推导出了径向分布高斯列阵光束通过湍流大气传输的二阶矩束宽和远场发散角的解析公式,并详细研究了大气湍流对光束扩展和方向性的影响.研究表明,相干合成情况下,子光束数N越小、径向分布半径r₀越大,列阵光束扩展受湍流影响越小.相干较非相干合成时列阵光束的扩展小,但非相干合成时列阵光束扩展受湍流的影响比相干合成时的小.特别地,N足够小或r₀足够大时,相干与非相干合成列阵光束的远场束宽相等.另一方面,还给出了相干和非相干合成径向分布高斯列阵 关键词： 径向分布高斯列阵光束 大气湍流 相干和非相干合成 二阶矩束宽     

非Kolmogorov大气湍流对高斯列阵光束扩展的影响

本文推导出了高斯列阵光束在非Kolmogorov大气湍流中传输的瑞利区间zR、湍流距离zT和远场发散角θ的解析表达式,研究了非Kolmogorov湍流的广义指数α和列阵光束的合成方式对高斯列阵光束扩展的影响.研究表明:不论相干还是非相干合成高斯列阵光束,zR,zT和θ均随着α的增加而呈非单调变化.当α=3.108时,zR和zT取极小值,而θ取极大值,即当α=3.108时高斯列阵光束扩展最厉害,光束扩展受湍流影响也最厉害.非相干合成高斯列阵光束扩展比相干合成的要大,但受非Kolmogorov湍流影响却要小.特别值得指出的是:当自由空间光束衍射较小时,有zTzR,即在瑞利区间范围内大气湍流就对光束扩展有影响;而当自由空间光束衍射较大时,有zTzR,即在瑞利区间范围内大气湍流对光束扩展几乎没有影响.     

大气湍流和热晕效应对列阵合成激光传输特性和光束质量影响的理论研究进展

介绍了大气湍流效应和热晕效应对列阵合成激光传输特性和光束质量影响的理论研究进展。主要介绍了合成激光在大气中传输的解析和数值模拟研究方法,大气湍流效应对列阵合成光束的光强分布、远场发散角、方向性、曲率半径和湍流距离的影响,以及大气热晕效应对列阵合成光束的光强分布、传输效率、重心偏移、热晕时间尺度和焦移的影响。研究结果表明,大气湍流效应和热晕效应对合成激光光束质量的影响与光束合成方式、合成光束参数以及大气参数密切相关。     

湍流对M×N列阵双曲余弦高斯光束传输和远场光束质量的影响

基于广义惠更斯-菲涅耳原理,并采用光束的非相干合成方法,推导出了M×N双曲余弦高斯列阵光束在湍流中的三维光强传输方程.采用桶中功率、β参量和Strehl比作为光束质量的评价参量,研究了湍流大气对双曲余弦高斯列阵光束远场光束质量的影响.研究表明:在湍流大气中,双曲余弦高斯列阵光束的传输将经历三个阶段的变化,并且湍流使得光束传输经历三阶段的进程加快;湍流导致双曲余弦高斯列阵光束扩展、最大峰值光强下降,但是,β参量随光束数目M(N)、相邻子光束间距xd(yd)和光束参量δ的增加而减少,即光束扩展受湍流的影响减小;并且,存在最佳xd(yd)和δ值使得Strehl比取得极大值.因此,适当选取M(N)、xd(yd)和δ可以降低湍流对双曲余弦高斯列阵光束远场光束质量的影响.     

湍流对M×N列阵双曲余弦高斯光束传输和远场光束质量的影响

基于广义惠更斯-菲涅耳原理,并采用光束的非相干合成方法,推导出了M×N双曲余弦高斯列阵光束在湍流中的三维光强传输方程．采用桶中功率、β参量和Strehl比作为光束质量的评价参量,研究了湍流大气对双曲余弦高斯列阵光束远场光束质量的影响．研究表明：在湍流大气中,双曲余弦高斯列阵光束的传输将经历三个阶段的变化,并且湍流使得光束传输经历三阶段的进程加快;湍流导致双曲余弦高斯列阵光束扩展、最大峰值光强下降,但是,β参量随光束数目M（N）、相邻子光束间距xc（yd）和光束参量δ的增加而减少,即光束扩展受湍流的影响减小;并且,存在最佳xd（yd）和δ值使得Strehl比取得极大值．因此,适当选取M（N）、xd（yd）和δ可以降低湍流对双曲余弦高斯列阵光束远场光束质量的影响．     

矩形分布高斯-谢尔模型列阵光束的等效曲率半径

 推导出矩形分布高斯-谢尔模型（GSM）列阵光束通过湍流大气传输的等效曲率半径的解析表达式。研究表明,等效曲率半径由湍流强度、GSM列阵光束参数及光束的叠加方式等因素共同确定。湍流使得等效曲率半径减小,但湍流对交叉谱密度函数叠加时等效曲率半径的影响要比光强叠加时大。在自由空间中,交叉谱密度函数叠加时GSM列阵光束的等效曲率半径要比光强叠加时的大。但是,随着湍流的增强,交叉谱密度函数叠加时GSM列阵光束的等效曲率半径可以大于、等于或小于光强叠加时的等效曲率半径。此外,若光束相干参数和子光束数目越大,则等效曲率半径受湍流的影响越大。GSM列阵光束的等效曲率半径受湍流的影响比高斯列阵光束要小。     

部分相干厄米高斯光束在斜程大气湍流中的扩展

基于广义惠更斯-菲涅耳原理,推导出部分相干厄米高斯（H-G）光束通过斜程大气湍流传输的均方根束宽和角扩展的解析表达式,并用以研究了传输路径和光束阶数对部分相干H-G光束传输的影响。引入相对束宽和相对角扩展来定量描述光束抗拒大气湍流的能力。结果表明:在相同条件下,部分相干H-G光束斜程传输受大气湍流的影响要小于水平传输,与水平传输相比斜程传输更有利于部分相干光束在大气湍流中的传输,光束阶数越大部分相干H-G光束受大气湍流的影响越小。     

湍流对M×N列阵双曲余弦高斯光束传输和远场光束质量的影响

基于广义惠更斯－菲涅耳原理,并采用光束的非相干合成方法,推导出了M×N双曲余弦高斯列阵光束在湍流中的三维光强传输方程.采用桶中功率、β参量和Strehl比作为光束质量的评价参量,研究了湍流大气对双曲余弦高斯列阵光束远场光束质量的影响.研究表明:在湍流大气中,双曲余弦高斯列阵光束的传输将经历三个阶段的变化,并且湍流使得光束传输经历三阶段的进程加快;湍流导致双曲余弦高斯列阵光束扩展、最大峰值光强下降,但是,β参量随光束数目M（N）、相邻子光束间距xd（yd）和光束参量δ的增加而减少,即光束扩展受湍流的影响减小;并且,存在最佳xd（yd）和δ值使得Strehl比取得极大值.因此,适当选取M（N）、xd（yd）和δ可以降低湍流对双曲余弦高斯列阵光束远场光束质量的影响.     

横向激发线偏振高斯光束的非傍轴传输

文章提出一种横向激发的任意线偏振高斯光束,该光束场量的模与传统的任意线偏振高斯光束具有相同的模,在源场区,其满足自由空间无源场的场方程。同时利用瑞利—索末菲衍射积分对该高斯光束的非傍轴传输特性进行了解析研究,给出了空间光强分布、束腰和远场发散角的解析通式,发现该类光束的远场光强呈一平顶空心光束。     

The directionality of partially coherent beams expressed in terms of the far-field divergence angle and of the far-field radiant intensity distribution

Taking the partially coherent cosh-Gaussian beam (ChG) as an illustrative example, the far-field divergence angle and directionality of partially coherent beams are studied. There are three competing physical mechanisms, i.e., the spatial coherence, diffraction and decentration, which affect the far-field divergence angle of partially coherent ChG beams. Two partially coherent ChG beams may generate the same far-field divergence angle, and partially coherent ChG beams may also have the same far-field divergence angle as a fully coherent ChG beam or as a fully coherent Gaussian laser beam if the three physical mechanisms are appropriately balanced. The consistency of the directionality of partially coherent beams expressed in terms of the far-field divergence angle and in terms of the far-field radiant intensity distribution is examined. Generally, two partially coherent beams with the same far-field divergence angle have not certainly the same far-field radiant intensity distribution. However, under certain conditions, it is possible to achieve the consistency of the directionality expressed in terms of the far-field divergence angle and of the normalized far-field radiant intensity distribution.     

Consistency of the directionality of partially coherent beams inturbulence expressed in terms of the angular spread and the far-field average intensity

Under the quadratic approximation of the Rytov's phase structure function, this paper derives the general closed-form expressions for the mean-squared width and the angular spread of partially coherent beams in turbulence. It finds that under a certain condition different types of partially coherent beams may have the same directionality as a fully coherent Gaussian beam in free space and also in atmospheric turbulence if the angular spread is chosen as the characteristic parameter of beam directionality. On the other hand, it shows that generally, the directionality of partially coherent beams expressed in terms of the angular spread is not consistent with that in terms of the normalized far-field average intensity distribution in free space, but the consistency can be achieved due to turbulence.     

非Kolmogorov大气湍流对部分相干厄米高斯光束传输因子的影响

基于非Kolmogorov谱模型,利用广义惠更斯-菲涅耳原理和维格纳分布函数的二阶矩定义,推导出部分相干厄米高斯(H-G)光束在非Kolmogonov大气湍流中传输因子的解析表达式,并用以研究了非Kolmogorov大气湍流对部分相干H-G光束传输因子的影响。结果表明,部分相干H-G光束在非Kolmogorov大气湍流中传输时,传输距离、湍流外尺度、广义结构常量和空间相关长度越小,湍流内尺度和光束阶数越大,光束传输受非Kolmogorov大气湍流影响越小,光束质量越好。当广义指数取3.11时,部分相干H-G光束在传输过程中表现的光束质量最差。     

Near-field and far-field spreading of partially coherent annular beams propagating through atmospheric turbulence

Based on the extended Huygens–Fresnel principle, closed-form expressions for the Rayleigh range and the far-field divergence angle of partially coherent annular beams propagating through atmospheric turbulence are derived by using the Wigner distribution function (WDF). Taking the Rayleigh range and the far-field divergence angle as the characteristic parameters of near-field and far-field spreading, respectively, the spreading of partially coherent annular beams both in free space and in turbulence is studied in detail. It is found that the effect of the strength of turbulence and beam parameters (e.g., the spatial correlation length, the waist width, and the wave length) on the beam spreading in the near field is in agreement with that in the far field. However, in turbulence, the effect of the obscure ratio of annular beams on the spreading is different between in the near field and in the far field. Namely, in turbulence the beam spreading in the near field becomes smaller and the beam spreading in the far field becomes larger as the obscure ratio increases. In particular, the effect of turbulence on the Rayleigh range and the far-field divergence angle is nearly unchanged versus the obscure ratio when the spatial correlation length is small. The main results obtained in this paper are explained physically.     

Influence of atmospheric turbulence on the propagation of superimposed partially coherent Hermite-Gaussian beams

The influence of atmospheric turbulence on the propagation of superimposed partially coherent Hermite-Gaussian (H-G) beams is studied in detail. The closed-form propagation equation of superimposed partially coherent H-G beams through atmospheric turbulence is derived. It is shown that the turbulence accelerates the evolution of three stages which superimposed partially coherent H-G beams undergo. The turbulence results in a beam spreading and a decrease of the maximum intensity. However, the larger the beam number M, the beam order m, the separate distance x_d, and the smaller the beam correlation length σ₀ are, the less the power focusability of superimposed partially coherent H-G beams is affected by the turbulence. Specially, superimposed partially coherent H-G beams are less sensitive to turbulence than superimposed fully ones, and than partially coherent H-G beams if the beam power focusability and the maximum intensity are taken as beam criterions. However, the maximum intensity of superimposed partially coherent H-G beams is less sensitive or more sensitive to turbulence than that of superimposed Gaussian Schell-model (GSM) beams depending on σ₀.     

Partially Coherent cosh-Gaussian Beams in Atmospheric Turbulence with the Same Directionality as a Laser

Directionality of a class of partially coherent cosh-Gaussian beams propagating in atmospheric turbulence is studied. It is shown that two partially coherent cosh-Gaussian beams may generate the same angular spread, and there exist equivalent partially coherent cosh-Gaussian beams which may have the same directionality as a fully coherent Gaussian laser beam in free space and also in atmospheric turbulence. The theoretical results are interpreted physically and illustrated numerically.     

双曲余弦高斯列阵光束通过湍流大气传输的角扩展及方向性

 采用积分变换,推导出了双曲余弦高斯（ChG）列阵光束通过湍流大气传输的二阶矩束宽和角扩展的解析公式,给出了ChG列阵光束与一束高斯光束具有相同角扩展的条件。研究表明:相干合成的ChG列阵光束的角扩展比非相干合成的小,但是,非相干合成的ChG列阵光束的角扩展受湍流影响比相干合成ChG光束小;相干合成情况下,ChG列阵光束的角扩展随离心参数、束腰宽度和相对子光束间距的变化均出现振荡,但在湍流中的振荡减弱,非相干合成情况下,ChG列阵光束的角扩展与相对子光束间距和光束数无关。