Propagating beams carrying orbital angular momentum through simulated optical turbulence generated by Rayleigh–Bénard natural convection

Abstract

Numerical simulations of Rayleigh–Bénard (RB) convective flow are performed to determine the optical and mechanical turbulence properties and resulting index of refraction field in order to study the propagation characteristics of a laser beam carrying orbital angular momentum. The simulations are carried out in air using a computational fluid dynamics package which solves the Navier-Stokes equations. The computational domain is 0.1 m × 0.5 m × 0.5 m with a temperature difference of 1°K maintained between the top and bottom plate. The simulated temperature field is then converted into refractive index values. To study light propagation through the turbulent volume the split-step screen method is employed with screens at 0.025 m distance from each other along the propagation path which ranges from 0.5 m to 2.5 m. The structure of the phase screens, their spatio-temporal correlation with respect to up/down drafts, and phase changes across regions of interest are discussed. It was observed as the propagation distance increased, the orbital angular momentum carrying Laguerre–Gaussian beams wandered and the beam phase singularity distorted thus impacting the light intensity distribution. In addition, it was found that higher topological charge and order of Laguerre polynomial result in increased distortion of the beam vortex.