Enhanced backscatter of vortex beams in double-pass optical links with atmospheric turbulence

Abstract

Though the enhanced backscatter (EBS) of waves passing through monostatic turbulence has been explored extensively over the past few decades, studies have been confined to spherical, planar, or Gaussian waves. Here we experimentally investigate the EBS of Laguerre–Gaussian (LG) vortex beams on double passage through turbulent air, reflecting from a retroreflector. It is found that only vortex beams with an even topological charge exhibit EBS, whereas beams with an odd topological charge maintain a dark-hollow shape. It is also found from observing instantaneous beam profiles that vortex modes can convert from LG to Hermite–Gaussian (HG) form. The physical mechanisms behind the aforementioned effects are explained using a ray model, and the results are further confirmed computationally using a multiple phase screen method. This work potentially allows the control of EBS through engineering the phase in the transmitter plane.