共查询到18条相似文献,搜索用时 203 毫秒
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对高能激光在大气中传输时产生的热晕效应及其相位补偿进行了室内仿真实验测量,获得了自适应光学系统开闭环时用来衡量光束传输效果参量(如远场的光斑图像、质心漂移、二阶矩半径、及Strehl比等)。结果表明,Bradley-Hermann热畸变参数在300范围内,自适应光学系统相位补偿效果显著,Strehl比基本大于0.4。然而随着热畸变效应的进一步加强,出现相位补偿不稳定性现象,补偿效果变差。另外,对自适应光学系统开闭环时的实验结果分别与薄透镜近似分析理论及几何光学近似理论作了比较。比较结果表明:薄透镜近似理论与未补偿时的实验结果吻合较好,而几何光学近似理论与补偿后的实验结果存在较大的偏差。 相似文献
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采用高能激光大气传输四维仿真程序模拟计算了高功率固态激光在非Kolmogorov湍流大气中聚焦传输时的湍流与热晕效应。数值分析了接收平面处光斑的63.2%环围能量半径、光束质量因子随非Kolmogorov湍流谱指数α和传输起伏强度D/r0的变化,比较了非Kolmogorov湍流与Kolmogorov湍流条件下激光传输结果的相对偏差。结果表明:非Kolmogorov湍流谱指数α越小,湍流效应和湍流热晕综合效应导致的光斑扩展越大,光束的能量集中度越低;已建立的描述聚焦高斯光束大气传输光束扩展的定标关系式在非Kolmogorov湍流条件下不再成立;在传输参数条件下,仅考虑湍流效应时,非Kolmogorov湍流与Kolmogorov湍流下光斑半径的相对偏差最大值可达87.7%,存在热晕时的最大相对偏差达43.7%,可见热晕降低了两种情况下传输结果的相对偏差。 相似文献
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本工作用包括热晕、湍流和风等效应的等压近似下四维激光传输程序,数值计算了激光大气传输中的整束热畸变效应及其理想相位补偿,得到了各种情况下的激光大气传输畸变图象,并分析了热晕和湍流的相互作用。另外,还讨论了时、空步长的选取原则。 相似文献
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旋转光束指的是一类由拓扑荷数不同的涡旋光束经外差干涉产生的,光强、相位或偏振随时间快速旋转的新型光束.旋转光束在大气通道传输时因其光场随时间快速旋转可遍历大气传输路径上的不均匀性,使得大气湍流和热晕等效应引起的相位畸变在旋转方向得到匀滑,从而达到改善光束质量,提升光束质心稳定性的目的.在考虑大气湍流和热晕综合效应的情况下,建立了旋转光束在大气的传输模型,分析了旋转光束如何缓解大气湍流和热晕效应的物理机制.在此基础上,进一步分析了光束旋转频率和子光束功率比值,以及大气湍流和热晕强度等对旋转光束大气传输特性的影响及规律,从而为激光大气工程应用提供参考. 相似文献
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激光在大气中传输时,由于强湍流或长传输距离的影响,畸变波前中出现由相位起点组成的不连续相位,现有波前复原算法不能有效复原不连续相位,使得自适应光学系统校正效果下降甚至失效.本文分析了最小二乘波前复原算法不能复原相位奇点的原因,提出了基于瀑布型多重网格加速的复指数波前复原算法,给出了复指数波前复原算法中迭代计算、降采样、插值计算的实现方式.研究了该方法对不连续相位和随机连续相位的复原能力,数值分析了采用复指数波前复原算法的自适应光学系统对大气湍流像差的校正效果.仿真结果表明,同等复原精度下,相比直接迭代过程,该方法所需浮点乘数目减少了近2个数量级,且随着夏克-哈特曼波前传感器子孔径数目增加,其在计算量上的优势更加明显. Rytov方差较大时,相比直接斜率法,自适应光学系统采用复指数波前复原算法后校正光束Strehl比提升1倍. 相似文献
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《光学学报》2015,(7)
利用数值模拟的方法研究了平面波在弱湍流大气中沿水平路径传播时的闪烁特性,得到了传播路径上既包含Kolmogorov湍流(简称K湍流)又包含非Kolmogorov湍流(简称非K湍流)时,平面波的闪烁指数与光传播距离、非K湍流谱标度指数、非K湍流所占百分比等参数之间的关系。对比分析了平面波在混合湍流路径下的闪烁效应与在单独K湍流和非K湍流下的闪烁效应。结果表明:当路径上湍流为K湍流和非K湍流的组合,且非K湍流谱一定时,闪烁指数随传播路径上非K湍流所占百分比的增加而增加,随K湍流所占百分比的增加而下降;当传播路径上只有非K湍流时,闪烁指数随非K湍流谱幂率的增加呈先增加后下降的趋势。 相似文献
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基于Taylor湍流冻结假设理论,在不同湍流折射率谱型条件下,推导得出了光波闪烁和相位起伏频谱的表达式;数值计算了湍流谱型中折射率标度指数、内尺度以及外尺度变化时对光波频谱的影响。结果表明:随着折射率起伏标度指数的增大,闪烁频谱的低频段不再仅为常数,高频段下降的幂率逐渐增大,同时相位频谱在整个起伏频率段下降的幂率越来越大;湍流内尺度的增加将引起光波频谱的高频段下降的幂率越来越大;而随外尺度的减小,闪烁频谱低频段的振幅减小,这种影响在大口径接收时较为明显,相位谱的低频段幂率减小。 相似文献
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Wenhe Du Jingxuan Yang Zhongmin Yao Junguo Lu Daosen Liu Quanling Cui 《Journal of Russian Laser Research》2014,35(4):416-423
Both increasing experimental evidence and some results of theoretical investigation have shown that there exist two kinds of turbulence in the aerosphere, Kolmogorov and non-Kolmogorov turbulence. Thus, it is necessary to improve the theory of optical wave propagation through atmospheric turbulence, namely, study the laser-beam propagation in non-Kolmogorov turbulence, before analyzing the joint influence of the Kolmogorov turbulence and non-Kolmogorov one on satellite laser communication. The beam wander will lead to the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, we consider a theoretical power spectrum of refractive-index fluctuations with a generalized power law in order to derive the variance of Gaussian-beam wave wander in weak turbulence for a horizonal path and analyze the influence of spectral power-law variations on the beam wander. We show that the expression for the beam-wander variance is of concise closed form and independent of the optical wavelength. 相似文献
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选取多种典型激光传输条件下的计算参量,对平台光束聚焦大气传输湍流热晕相互作用引起的光束扩展进行了数值分析.热畸变的产生是在快速变化的湍流扩束作用之后,在此假定的基础上,建立了描述聚焦光束大气传输光束扩展与大气传输特征物理参量的定标关系.在了解激光发射系统的特征参量和大气传输效应的特征参量之后,即可由定标关系迅速判断激光大气传输的效果,从而为激光工程系统的参量优化设计及其应用效能评估提供依据.
关键词:
湍流效应
热晕效应
光束扩展
定标规律 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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《Waves in Random and Complex Media》2013,23(4):743-758
ABSTRACTIt is well known that in free atmosphere the Kolmogorov power spectrum of the refractive index might not properly describe the actual turbulence behavior. In this paper, we use general non-Kolmogorov power spectrum for theoretical investigation of laser beam propagation in the double-passage problem: transmitter–target–receiver. The major application of our work is the Light Detection And Ranging (LIDAR) system operating at high altitudes, where non-Kolmogorov turbulence may be present. On confining ourselves to the weak turbulence regime, we show that the long-term average beam intensity profile, the long-term beam spread and the scintillation index are substantially affected by the non-Kolmogorov turbulent channels. Our analysis is valid for both bi-static and mono-static configurations, the latter leading to the enhanced backscattering effects. 相似文献
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Wenhe Du Hengjun Zhu Daosen Liu Zhongmin Yao Chengjiang Cai Xiufeng Du Ruibo Ai 《Journal of Russian Laser Research》2012,33(5):456-463
In the past half a century, satellite laser communication has caught the attention of scientists due to its distinct advantages in comparison with conventional satellite microwave communication. For ground-to-satellite and satellite-to-ground data links, the atmosphere is a part of the communication channel; thus, atmospheric turbulence severely degrades the performance of satellite laser communication systems. In general, the Kolmogorov turbulence model is used to study the effect of atmosphere turbulence on satellite laser communications since it has been confirmed by numerous direct measurements of temperature and humidity fluctuations in the atmospheric boundary layer. However, increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes inadequate to describe atmospheric statistics properly, in particular, in some domains of the atmosphere. We analyze the joint influence of Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the spot size associated with the uplink and downlink propagation channels for a satellite laser communication system in the geosynchronous orbit, using a power spectrum of non-Kolmogorov turbulence with power law ?5 that describes the refractiveindex fluctuations in the atmosphere above 6 km and considering the combined power spectrum of Kolmogorov and non-Kolmogorov turbulence. Before this analysis, we study the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams. 相似文献
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Wenhe Du Zhongmin Yao Daosen Liu Chengjiang Cai Xiufeng Du Ruibo Ai 《Journal of Russian Laser Research》2012,33(1):90-97
Satellite laser communication holds the potential for high-bandwidth communication, but the atmosphere can significantly affect
the capability of this type of communication systems for satellite-toground and ground-to-satellite data links to transfer
information consistently and operate effectively. Usually the influence of atmosphere on satellite laser communication is
investigated based on the Kolmogorov turbulence model. However, both increasing experimental evidence and theoretical investigations
have shown that the Kolmogorov theory is sometimes incomplete to describe the atmospheric statistics properly, in particular,
in some portions of the atmosphere. Considering a non-Kolmogorov turbulent power spectrum with power law −5 that describes the refractive-index fluctuations in the atmosphere above 6 km, we calculate the scintillation index of a
lowest-order Gaussian-beam wave under the weak-fluctuation condition. Then, considering a combined power spectrum of refractiveindex
fluctuations and using the expression obtained, we analyze the joint influence of the Kolmogorov turbulence from the ground
to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams used in ground-to-satellite and
satellite-to-ground laser communication links. We show that the scintillation index in satellite laser communication is equal
to the sum of the scintillation indices induced by the Kolmogorov turbulence from ground to 6 km and that caused by the non-Kolmogorov
turbulence above 6 km. Also we investigate variations of the scintillation index with the beam radius on the transmitter,
wavelength, the radial distance, and zenith angle. Finally, comparing the scintillation index induced by these two turbulences
with the conventional results, we show that the scintillation index induced by these two turbulences is a bit smaller than
the conventional results. 相似文献