共查询到18条相似文献,搜索用时 171 毫秒
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当光波在大气中传播时,由于大气湍流的作用,其光束质量将会极大地恶化。对于这类问题的处理,长期以来都是以Tartaskii等人的理论为指导,而他们的理论是根据Kolmogrov于1941年建立的局地均匀各向同性湍流理论(K41)建立的,所以K41理论是这一领域奠基的基石。然而,随着湍流研究的深入,人们已经逐渐意识到K41湍流理论的各方面的缺点,其中尤其明显的是,K41理论忽略了湍流的间歇特征。在湍流现代理论中,湍流间歇性的研究一直是处于中心位置。经过数十年的不懈的努力,目前人们已经对湍流间歇性有了一些初步的成果和认识。本文综述了试图将湍流间歇性引入随机介质中光传播问题的考虑之中的各种尝试。我们首先结合光学问题的需要对湍流及其间歇性研究现状及重要成果进行了概要的回顾和说明。在此基础上,我们以两种方式对间歇性大气湍流中光传播问题进行分析:首先,我们以一种简单的非Gauss场模型为基础分析间歇性大气湍流中的光场统计性质;然后,我们将统计矩方程展开到四阶累积函数,分析了近Gauss场附近的光场统计性质。我们还以层次结构模型为基础对二阶统计矩进行了进一步的研究。 相似文献
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当光波在大气中传播时,由于大气湍流的作用,其光束质量将会极大地恶化。对于这类问题的处理,长期以来都是以Tartask ii等人的理论为指导,而他们的理论是根据Kolmogrov于1941年建立的局地均匀各向同性湍流理论(K41)建立的,所以K41理论是这一领域奠基的基石。然而,随着湍流研究的深入,人们已经逐渐意识到K41湍流理论的各方面的缺点,其中尤其明显的是,K41理论忽略了湍流的间歇特征。在湍流现代理论中,湍流间歇性的研究一直是处于中心位置。经过数十年的不懈的努力,目前人们已经对湍流间歇性有了一些初步的成果和认识。本文综述了试图将湍流间歇性引入随机介质中光传播问题的考虑之中的各种尝试。我们首先结合光学问题的需要对湍流及其间歇性研究现状及重要成果进行了概要的回顾和说明。在此基础上,我们以两种方式对间歇性大气湍流中光传播问题进行分析:首先,我们以一种简单的非Gauss场模型为基础分析间歇性大气湍流中的光场统计性质;然后,我们将统计矩方程展开到四阶累积函数,分析了近Gauss场附近的光场统计性质。我们还以层次结构模型为基础对二阶统计矩进行了进一步的研究。 相似文献
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湍流大气中高斯谢尔光束的波前位错 总被引:12,自引:12,他引:0
在Rytov近似下,通过引入短期统计平均位错位置的概念,研究了高斯谢尔光束通过近地面弱湍流大气传播时,波前圆形位错形成和位错位置与湍流大气起伏强度和传播距离等参数间的关系.基于湍流大气中平行和交叉双光束的简化近似传输模型,研究了湍流大气中传播高斯谢尔光束波前位错位置与大气湍流强度、传输距离等参数间的相关机制.在远小于光波位相起伏周期的条件下,分别得出了束径不同同轴双光束和交叉双光束传播情况下波前圆位错位置的湍流系综统计平均理论关系.所得结果表明,同轴平行光束干涉和交叉光束干涉所产生的光束波前位错受大气湍流强度、传输距离等参数调制的规律是不同的. 相似文献
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湍流路径积分参量与湍流大气中光的传播效应 总被引:5,自引:1,他引:4
根据光波在湍流大气中传播的理论分析了弱起伏条件下决定光波传播效应的折射率结构常数C^2n的各种路径积分参量之间的关系,导出了由光波的强度起伏所确定的等效折射率结构常数对计算大气相干长度与光波的到达角起伏,光束的扩展及漂移的相对偏差的表达式。针对折射率结构常数C^2n具有周期性,递减,递增和随 相似文献
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大气湍流对光波传播的影响主要是由于大气随机起伏的湍流引起折射率的随机起伏,破坏了光波的相干性。研究传输问题就是研究湍流所造成的折射率随机变化的规律。主要利用HTP-2型温度脉动探空仪对大气折射率结构常数进行了实地探测及计算分析。通过对大量探空实验数据的统计分析,分别得出了合肥地区和北方干旱地区(0~30km)大气折射率结构常数在不同季节的白天和夜间的分布廓线和分布特性,对合肥地区和北方干旱地区的大气湍流结构特性有了比较清晰的认识,为大气光学传输工程的应用和理论计算提供了参考。 相似文献
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根据推广的惠更斯-菲涅尔原理及ITU-R大气结构常数模型(2001年国际电信联盟提出的随高度变化的大气结构常数模型),考虑了大气湍流对激光从发射机到目标和从目标到接收机双程路径的影响,研究了大气湍流中漫射目标的激光波束散射问题,导出了考虑对数振幅起伏和相位占优情况下在斜程大气湍流中传输时激光波束散射场的互相关函数、强度协方差和强度方差的计算公式,并给出了数值计算结果.数值分析了波长、接收机高度和传播距离对强度协方差和归一化强度方差的影响.
关键词:
激光散射
斜程湍流
强度方差
强度协方差 相似文献
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湍流大气传输高斯谢尔光束的到达角起伏 总被引:13,自引:10,他引:3
研究了在弱大气湍流起伏环境下以窄带宽高斯谢尔光束为激光光源的大气通信问题,分析了大气湍流强度和光源空间相干度对通信光束到达角起伏的影响.采用窄带宽光场的交叉谱密度函数代替光场互相干函数的近似方法和采用包含大气湍流内外尺度的简化折射率谱密度函数,得出了湍流大气中传输高斯谢尔光束的波结构函数(WSF) 和到达角起伏方差解析近似关系.分析表明,光源的空间相干度和传输光束的湍流扩展是影响高斯谢尔光束的相位起伏结构函数和传输光束到达角起伏的重要因素. 相似文献
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非柯尔莫哥洛夫湍流光束漂移的理论研究 总被引:1,自引:0,他引:1
一直以来, 大气湍流对空间光通信影响的研究都是在柯尔莫哥洛夫(Kolmogolov)湍流理论的框架内进行, 该模型已经被人们广泛接受和使用。然而, 近年来国内外众多非柯尔莫哥洛夫(Non-Kolmogolov)湍流的实验报道则表明Kolmogolov湍流理论有时不能完全正确地描述大气湍流的统计规律, 尤其在对流顶层和平流层。为了全面了解大气湍流对空间光通信的影响, 研究Non-Kolmogolov湍流对光波传输的影响成为了首先要面对的问题。基于Non-Kolmogolov湍流功率谱密度, 运用几何光学近似方法推导了弱起伏条件下准直光束和聚焦光束的光束漂移方差, 并给出了简洁的解析表达式; 然后, 利用这一表达式进行了仿真分析。 相似文献
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A new tomographic method for the measurement of three-dimensional refractive-index fields of transparent media, which we call holographic coherence tomography and which combines double-exposure holographic interferometry with the detecting style of optical coherence tomography, has been developed. The three-dimensional refractive-index field can be achieved with a confocal lens system by continual longitudinal and horizontal scanning of the holographic reconstruction image. 相似文献
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Yi Dong Yuming Sun Yufei Li Xiaoqiang Yu Xueyuan Hou 《Optics & Laser Technology》2007,39(8):1522-1527
Based upon equivalent transmission line method, a perturbation analysis on the guiding properties of refractive-index gratings is presented. By numerical calculation, the leakage parameter which influences the leakage energy into the diffracted orders due to the grating scatter, is achieved as functions of the grating period, thickness of the waveguide and index modulation Δn. Our results reveal that, although the index modulation Δn is much less than that of the etched or deposited grating, refractive-index gratings can still reach a high leakage parameter because of the prominent increase of the grating height. 相似文献
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A. Ródenas G. A. Torchia G. Lifante E. Cantelar J. Lamela F. Jaque L. Roso D. Jaque 《Applied physics. B, Lasers and optics》2009,95(1):85-96
The effect that femtosecond laser filamentation has on the refractive index of Nd:YAG ceramics, and which leads to the formation
of waveguide lasers, has been studied by micro-spectroscopy imaging, beam propagation experiments and calculations. From the
analysis of the Nd3+ luminescence and Raman images, two main types of laser induced modifications have been found to contribute to the refractive-index
change: (i) a lattice defect contribution localized along the self-focusing volume of the laser pulses, in which lattice damage
causes a refractive-index decrease, and (ii) a lattice strain-field contribution around and inside the filaments, in which
the pressure-driven variation of the inter-atomic distances causes refractive-index variations. Scanning near-field optical-transmission
and end-coupling experiments, in combination with beam propagation calculations, have been used to quantitatively determine
the corresponding contribution of each effect to the refractive-index field of double-filament waveguides. Results indicate
that the strain-field induced refractive-index increment is the main mechanism leading to waveguiding, whereas the damage-induced
refractive-index reduction at filaments leads to a stronger mode confinement. 相似文献
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单光子源通常采用基于高斯光束的高度衰减激光脉冲,假设激光束具有初始高斯时域脉冲波形和TEM01模拉盖尔-高斯空域分布.基于折射率起伏的Rytov近似和修正von Karman谱模型,研究了大气湍流对星地量子通信单光子捕获概率的影响;建立了上行信道和下行信道的单光子捕获概率理论模型;针对低轨卫星-地面站间激光链路,对单光子捕获概率进行了分析.结果表明:上行信道的单光子捕获概率强烈依赖于地面折射率结构常数C2n(0),且随着C2n(0)的增加而减小;然而,下行信道的单光子捕获概率并不依赖于C2n(0),即大气湍流对其没有影响. 相似文献
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Polarization properties of single photon states propagating through the non-Kolmogorov turbulence in a slant channel are studied based on the degree of polarization of quantum field. The degree of polarization of single photon states for linearly polarized quantum beam propagation in a slant turbulent channel are developed. Our results show that the effects of the outer scale fluctuations of atmospheric turbulence and the wavelength difference of the beams on the polarization can be ignored and the smaller inner scale of turbulence and larger zenith angle of communication channel will lead to larger fluctuations of the polarization of single-photon states. The effects of the inner scale of turbulence on polarization of single photon states are more significant for bigger refractive-index power and bigger zenith angles. 相似文献
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The initiation and propagation of a filament generated by ultrashort laser pulses in turbulent air is investigated experimentally. A filament can be generated and propagated even after the beam has propagated through strongly turbulent regions, with structure parameters C(n)2 as many as 5 orders of magnitude larger than those encountered in the usual atmospheric conditions. Moreover, the filament's position within the beam is not affected by the interaction with a turbulent region. This remarkable stability is allowed by the strong Kerr refractive-index gradients generated within the filament, which exceed the turbulence-induced refractive-index gradients by 2 orders of magnitude. 相似文献
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Hernández JA Clark M Sharples SD Somekh MG Lopez VH 《The Journal of the Acoustical Society of America》2007,121(3):1396-1405
Materials that consist of a random microstructure can affect ultrasonic measurements--reducing signal strength, increasing noise, and reducing measurement accuracy--through scattering and aberration of the acoustic field. To account for these adverse effects a phase screen model, alongside the stochastic wave equation, has been developed. This approach allows the field and study aberrations to be modeled from a statistical point of view. Experimental evidence of aberration and statistical properties of the measured acoustic field are shown. A measured correlation function of the acoustic field is interlinked to mean crystallite size by using a theoretical coherence function that can be mainly described by the correlation length and wave velocity variation of microstructure. The estimation of the mean crystallite size using this technique would provide some insight into material characterization. 相似文献