Mitigation of thermal blooming by rotating laser beams in the atmosphere

Qiu, Die; Tian, Bian; He, Tengbing; Zhong, Zheqiang; Zhang, Bin

doi:10.1364/ao.438485

Cited by 11 publications

(2 citation statements)

References 26 publications

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“…[ [1,2]] ，一直是激光大气工程应用领域的核心问题。大气介质时空分布的不均匀性和各向异性会导致光束质量退化 [3] ，而热晕 [[4-6]] 则是一种由于大气介质对光束能量的吸收而导致的"负透镜效应"。长期以来，研究人员主要采用自适应光学技术 [7] 来抑制大气扰动带来的光束质量退化。然而，受限于系统造价和复杂度，自适应光学技术多应用于天文望远镜和显微成像 [8] 等。近年来，以涡旋光束、贝塞尔光束、艾里光束为代表的空间结构光束 [9] ，因其无衍射、自愈等特性为改善激光大气传输特性提供了新的解决思路和途径。然而，空间结构光束的传输性能随着传输距离的增大也逐步退化。因此，发展抗大气湍流和热晕效应的新型光束及其调控手段仍是研究热点之一。在我们所提出的利用旋转光束缓解大气湍流方案 [10,11] 中，通过使用相位快速旋转的光束，可在湍流特征时间范围内使其遍历大气通道横截面内的非均匀性和各向异性，使激光束的光束质量得到显著提高。这一相位快速旋转的光束可由拓扑荷数不同的涡旋光束经外差干涉产生，其旋转频率与外差频率相同。在泰勒湍流冻结假设 [12] 下，当旋转光束的旋转周期远小于湍流特征时间时可认为大气介旋转光束可由两束具有不同拓扑荷数 l a,b 的涡旋光束经外差干涉产生，经电光调制 [16] 或声光调制 [17] 等调制后，两涡旋光束的中心圆频率分别为 a,b ，则其合成光场可表示为：…”

Section: 引言如何克服大气湍流、热晕等效应引起的光束漂移、扩展和闪烁等现象unclassified

Propagation characteristics of rotating beams under combined effect of atmospheric turbulence and thermal blooming

Zhong¹,

Xiang²,

Zhang³

et al. 2023

Acta Phys. Sin.

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The rotating beam is such a beam that is generated by the heterodyne interference of vortex beams with different topological charges, whose intensity and wavefront rotate rapidly with time. Under Taylor’s frozen air hypothesis, such a rotating beam, whose rotating period is much shorter than the characteristic time of atmospheric turbulence and the thermal blooming, can travel through all the inhomogeneities due to its rapid rotation during its propagation in the air. The rotation can contribute to the smooth of the wavefront distortion caused by the atmospheric turbulence and the thermal blooming, and thus improve the beam quality and reduce the centroid drift of the rotating beam in far field. The physical model of rotating beam is established by the heterodyne interference of two vortex beams. Taking the atmospheric turbulence and the thermal blooming effect into consideration, the propagation model of the rotating beam in the air was established using the Split-Step Fourier Method (SSFM). For simplicity without generality, the influences of the atmospheric turbulence and the thermal blooming effect on the propagation of rotating beam, are both treated as wavefront screen. The difference is that, the wavefront screen of atmospheric turbulence is generated by the Kolmogorov power spectrum, while that of thermal blooming is generated by the fluid mechanics equation. The physical mechanism of how the rotating beam mitigate the atmospheric turbulence and the thermal blooming effect has been analyzed in detail, that is, when the laser beam rotates faster than the airflow, the laser beam can travel all the inhomogeneities and anisotropies of atmosphere in azimuthal direction within the time interval of airflow. After the laser propagates through the frozen air, the total wavefront distortion in the azimuthal direction becomes centrosymmetric with lower PV value, reducing the beam quality degradation. On the basis, the influence of rotation frequency, power ratio of the sub beams, strength of turbulence and thermal blooming on the propagation characteristics of the rotating beam in atmosphere have been analyzed. Within a certain range, as the beam rotation frequency increases, the mitigation effect of the rotating beam on atmospheric turbulence and thermal blooming effects is enhanced. With the increase of turbulence intensity and thermal blooming intensity, the mitigation effect of the rotating beam is weakened but still can maintain well, which can provide reference for the engineering applications of laser beam in atmosphere.

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Section: 引言如何克服大气湍流、热晕等效应引起的光束漂移、扩展和闪烁等现象unclassified

Propagation characteristics of rotating beams under combined effect of atmospheric turbulence and thermal blooming

Zhong¹,

Xiang²,

Zhang³

et al. 2023

Acta Phys. Sin.

View full text Add to dashboard Cite

show abstract

“…Zhao等 [19] 发现热晕效应会破坏单模涡旋光束初始螺旋相位分布, 大气传输后光强出现不对称分布. Maxim 等 [20] 研究表明具有分数阶拓扑电荷叠加的矢量光束在热晕效应中具有更明显的稳定性. 最近, 有研究者发现用涡旋光束相干叠加形成的旋转光束可减小热晕效应对光束质量的影响 [21,22] .…”

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Influence of wind-dominated thermal blooming on orbital angular momentum and phase singularity of dual-mode vortex beams

Xu,

Li,

Tang

et al. 2023

Acta Phys. Sin.

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The influence of thermal blooming on orbital angular momentum (OAM) and phase singularity of dual-mode vortex beams under different wind direction and wind speed has been studied in this paper. Due to the different symmetries of dual-mode vortex beams superimposed by different modes, the impact of thermal blooming on them not only depends on wind speed, but also on wind direction. Based on the scalar wave equation and the hydrodynamic equation, a 4D computer code to simulate the time-dependent propagation of dual-mode vortex beams in the atmosphere is devised by using the multiphase screen method and finite difference method. It is found that, for certain wind direction, the value of OAM increases with the decreasing wind speed because the thermal blooming becomes more serious, i.e., the thermal blooming effect promotes the OAM of dual-mode vortex beam growth. For an example, when the angle between the wind direction and the beam is 0＜<i>θ</i>＜50°, the OAM of the dual-mode vortex beams with a topological charge difference of 2 increases with decreasing wind speed, and there is an optimal angle (<i>θ</i>≈20°) to maximize OAM. Therefore, for certain wind direction and wind speed, the OAM of dual-mode vortex beam propagating in the atmosphere could be larger than that in free space, and could be larger than the OAM of single-mode vortex beam. The dual-mode vortex beam with higher modes requires smaller wind speed to make its OAM larger than the OAM in free space. In addition, the larger the topological charge difference between the two element beams of a dual-mode vortex beam is, the more stable the OAM of the dual-mode vortex beam is. On the other hand, the evolution of linear edge dislocation singularity under atmospheric thermal blooming are also investigated in this paper. When the wind direction is perpendicular to the dislocation line, the linear edge dislocation singularity disappears. If the wind direction is parallel to the dislocation line, the linear edge dislocation singularity always exists. At other angles, the linear edge dislocation singularity will evolve into optical vortex pairs. The results obtained in this paper are useful to laser propagating in the atmosphere and optical communication.

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Influence of thermal blooming on characterizations of general astigmatism laser beams propagating in the atmosphere

Tang,

Li,

Deng

et al. 2023

Opt Quant Electron

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Mitigation of thermal blooming by rotating laser beams in the atmosphere

Cited by 11 publications

References 26 publications

Propagation characteristics of rotating beams under combined effect of atmospheric turbulence and thermal blooming

Propagation characteristics of rotating beams under combined effect of atmospheric turbulence and thermal blooming

Influence of wind-dominated thermal blooming on orbital angular momentum and phase singularity of dual-mode vortex beams

Influence of thermal blooming on characterizations of general astigmatism laser beams propagating in the atmosphere

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