Rasouli Saifollah, Bagheri Mohammad, Niemela J J
Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, 45137-66731, Iran.
Optics Research Center, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, 45137-66731, Iran.
Sci Rep. 2024 Aug 8;14(1):18419. doi: 10.1038/s41598-024-69443-y.
In this study, we report observations of propagating radial carpet beams (RCBs) through a turbulent atmosphere at ground level with a 120 m path length. RCBs are a class of nondiffracting, accelerating, self-healing, and self-amplifying beams, and generated in the diffraction of a plane wave from amplitude/phase radial gratings having different spoke numbers. Observations were made at different times of the day. The intensity profile of an RCB becomes complicated when the number of grating spokes used to generate the beam is large, and includes high intensity spots, called main intensity spots (MISs), which are symmetrically placed at the central area around the beam axis and whose number is equal to (twice) the number of spokes of the amplitude (phase) grating used to generate the beam. With the aid of a telescope and a CCD camera, successive frames of the intensity pattern of the RCBs having different levels of structural complexity are recorded at the end of the path. For the data recorded at different times of the day, we calculate the variance of displacements of MISs along the radial direction. We observe that displacements of the MISs increase with increasing mean temperature of the air; on the other hand, as the complexity of the beam intensity pattern increases, the displacements of the MISs decrease. In order to compare the resilience of different RCBs and a well-known structured beam against atmospheric turbulence, we investigate deformation of the intensity profiles of a Laguerre-Gaussian (LG) beam having a topological charge 20 and different RCBs at the end of the path. It is shown that under the same turbulence condition, highly complex RCBs are more resilient to the destructive effects of the atmospheric turbulence. In particular, for the RCBs generated with gratings having 30 spokes and more, the number of MISs of the received intensity patterns is changed by less than 1% even when the turbulence strength is high. But for the LG beam, its intensity ring is clearly broken in different places, which makes it impossible to follow its maximum intensity in the radial direction.
在本研究中，我们报告了在地面水平上通过120米路径长度的湍流大气传播的径向地毯光束（RCB）的观测结果。RCB是一类无衍射、加速、自愈和自放大光束，由平面波从具有不同辐条数量的振幅/相位径向光栅衍射产生。观测在一天中的不同时间进行。当用于产生光束的光栅辐条数量很大时，RCB的强度分布会变得复杂，并且包括高强度光斑，称为主强度光斑（MIS），它们对称地位于光束轴周围的中心区域，其数量等于（两倍）用于产生光束的振幅（相位）光栅的辐条数量。借助望远镜和电荷耦合器件（CCD）相机，在路径末端记录了具有不同结构复杂度水平的RCB强度图案的连续帧。对于在一天中不同时间记录的数据，我们计算了MIS沿径向方向的位移方差。我们观察到，MIS的位移随着空气平均温度的升高而增加；另一方面，随着光束强度图案复杂度的增加，MIS的位移减小。为了比较不同RCB和一种著名的结构化光束对大气湍流的弹性，我们研究了在路径末端具有拓扑电荷20的拉盖尔 - 高斯（LG）光束和不同RCB的强度分布的变形。结果表明，在相同的湍流条件下，高度复杂的RCB对大气湍流的破坏作用更具弹性。特别是，对于由具有30个及以上辐条的光栅产生的RCB，即使湍流强度很高，接收强度图案的MIS数量变化也小于1%。但对于LG光束，其强度环在不同位置明显断裂，这使得无法在径向方向上跟踪其最大强度。
