Propagation of Laguerre-Gaussian and Im-Bessel beams through atmospheric turbulence: A computational study

The study of light carrying complex phase profiles, specifically orbital angular momentum (OAM), has been of interest for its use in free-space optical communications and remote sensing systems. Each of these applications requires a beam to propagate through the atmosphere, where optical turbulence is the main distorter of the beam. In this computational study, coherent Laguerre-Gaussian (LG) beams and partially coherent Im Bessel beams are propagated through atmospheric turbulence. The LG beams are propagated through turbulence using a split-step method for solving the Fresnel diffraction integral. Whereas for the the Im Bessel beams, the coherent mode representation is used, where each eigenmode is individually propagated through turbulence. The split-step algorithm is then modified to simulate optical turbulence by the use of phase screens. Beam metrics, in the form of intensity, scintillation, spot size, and OAM spectrum, are then calculated over a number of turbulence realizations. Three turbulence regimes are simulated that include the weak, moderate, and strong turbulence regimes along with two different initial beam sizes. The Im Bessel beam is simulated using three values of overall coherence ξ. The results for the metrics are plotted against propagation distance and OAM mode l. The resulting beam metrics show a strong dependence on turbulence strength, a weak dependence on OAM mode due to LG modes expanding with an extra prefactor of ι + 1, and no strong dependence on the overall coherence ξ.