Speckle characteristics of vortex beams scattered from rough targets in turbulent atmosphere

In this study, the echo speckle characteristics of the Laguerre-Gauss (LG) vortex beams scattered from random rough surface targets were examined based on the Rytov Approximation Theory. In addition, the expressions of the intensity correlation and coherence functions, along with the normalized intensity variances of the speckle fields, were derived. The coherent lengths and scintillation indexes of the speckle fields were then numerically simulated, and the speckle characteristics of the Laguerre-Gauss vortex beam were compared with those of the Gaussian beams. The effects of the topological charges, rough target radii, initial beam radii, turbulence intensities, and roughness degrees of the targets on the speckle characteristics of the LG vortex beams were analyzed. This study's results showed that in the weak turbulence regions, the target characteristics were the main influencing factors of the speckle fields. Meanwhile, in the strong turbulence regions, the turbulence effects were the main influencing factors of the speckle fields. The influence effects of turbulent atmosphere and target characteristics on the coherent lengths and scintillation effects of the vortex beam echoes were observed to be less than those of the Gaussian beams. In addition, the influence effects of the turbulent atmosphere on coherent lengths and scintillation effects of the vortex beams echoes with small topology were found to be minimal. Therefore, this study's results can potentially provide theoretical and technical guidance for the future applications of laser target detection, target recognition, and speckle measurement processes in space.