Phase fluctuations in vortex beams

Abstract

Phase fluctuations of vortex beams are examined using the random phase screen setup. By taking Gaussian, Bessel Gaussian and Laguerre Gaussian vortex beams, with the main focus being on Gaussian vortex beam, we investigate the phase fluctuations in a region around on-axis. These phase fluctuations are quantified in terms of phase variance and phase structure function. Variations of phase fluctuations against some of the source parameters, propagation distance and receiver plane radial position are plotted. Our analysis shows that the studied vortex beams have more phase fluctuations on and around the on-axis region in comparison to Gaussian beam. This is reflected into the phase variance of the vortex beams starting approximately aroundπfollowed by a fall. Similar trend applies to the phase structure function which exhibits a rapid increase just past the on-axis point. These observations change however at longer propagation distances where strong turbulence characteristics prevail. Here we observe saturation regimes, whereby all phase variances and structure functions settle around π and 2π respectively.