Experimental investigation on propagation characteristics of vortex beams in underwater turbulence with different salinity
doi: 10.37188/CO.EN.2021-0001
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摘要: 研究光束在海洋湍流中的传输特性尤为重要。为了更贴近实际情况，人工搭建了能控制水下湍流强度和盐度的装置来研究涡旋光束和高斯光束在水下湍流中的传输特性。结果表明：相比于未添加海盐的水下湍流，光束在增添海盐的水下湍流中传输光斑会更加弥散，光强会更弱。无论是强湍流还是弱湍流，m=2的涡旋光束在盐度为4.35‰的水下湍流中的闪烁因子都大于其在盐度为2.42‰的水下湍流中所对应的闪烁因子。另外，m=2的涡旋光束传输到相同的距离时，其闪烁因子随着水下湍流的盐度和强度的增大而增大。不同盐度条件下，m=2的涡旋光束的径向闪烁因子随径向距离的增大呈先减小后增大的变化趋势。另外，搭建了传输距离更长的实验装置，在20米的传输距离内，拓扑电荷m=2的涡旋光束的闪烁因子远高于高斯光束所对应的闪烁因子，且m=2的涡旋光束和高斯光束的闪烁因子都随着传输距离的增大而增大。Abstract: It is very important to study the propagation characteristics of light beams in ocean turbulence. In order to get closer to the actual situation, we build a device which can control both the salinity and the intensity of underwater turbulence to study the propagation characteristics of vortex beams and a Gaussian beam in underwater turbulence. The results show that compared with the underwater turbulence without sea salt, the light spot will be more diffuse and the light intensity will be weaker in the underwater turbulence with sea salt. When the topological charge m is 2, the scintillation index of the vortex beam in the underwater turbulence with salinity of 4.35‰ is larger than that in the underwater turbulence with salinity of 2.42‰, no matter it is strong turbulence or weak turbulence. When the vortex beam with m=2 propagates to the same distance, the scintillation index increases with the increment of the salinity and the intensity of underwater turbulence. Under different salinity conditions, the radial scintillation index of the vortex beam with m=2 decreases firstly and then increases with the increase of the radial distance. In addition, we set up another experimental device which can transmit a longer distance. The scintillation index of the vortex beam with m=2 is much higher than that of the Gaussian beam in the underwater turbulence within 20 m propagation distance, and the scintillation indices of both the vortex beam with m=2 and the Gaussian beam increase with the increase of the propagation distance.
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Key words:
- vortex beam /
- underwater turbulence /
- scintillation index /
- salinity /
- propagation
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Figure 1. Schematic diagram of vortex beams propagating in underwater turbulence. L1, L2, thin lenses; SPP, spiral phase plate; M1, M2, reflectors
Figure 2. The practical photos of the experimental device. (a) Weak turbulence; (b) strong turbulence
Figure 3. The scintillation of the vortex beam with m=2 transmitted to 3.6 meters in weak underwater turbulence with the SA =2.42 ‰
Figure 4. The intensity patterns of the vortex beam with m=2 propagating in both the weak and strong underwater turbulences with salinity of 0. (a) z=3.6 m, weak turbulence; (b) z=3.6 m, strong turbulence; (c) z=5.4 m, weak turbulence;(d) z=5.4 m, strong turbulence
Figure 5. The intensity patterns of the vortex beam with m=2 propagating in both the weak and strong underwater turbulences with the salinity of 2.42 ‰. (a) z=3.6 m, weak turbulence; (b) z=3.6 m, strong turbulence; (c) z=5.4 m, weak turbulence; (d) z=5.4 m, strong turbulence
Figure 6. Scintillation index of the vortex beam with m=2 varying with propagation distance in the water turbulence with different salinities in (a) weak turbulence and (b) strong turbulence
Figure 7. The effect of salinity on scintillation index of the vortex beam with m=2 at 3.6 m propagation distance in (a) weak turbulence and (b) strong turbulence
Figure 8. Scintillation index of the vortex beam with m=2 at 3.6 m propagation distance in (a) weak turbulence and (b) strong turbulence
Figure 10. Scintillation indices of the vortex beam and the Gaussian beam varying with propagation distance (no turbulence)
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