Gaussian component of beams with fractional topological charge

Abstract

Fractional vortex beams, which possess fractional topological charge ℓ, are interesting for allowing finer control of orbital angular momentum (OAM). In this paper, we characterize these kinds of beams by projecting them onto a Gaussian mode. We generated beams with fractional ℓ using an SLM and passed them into a single mode fiber, recording the magnitude of the exiting beam as voltage. We observe that this voltage is maximum for a Gaussian beam (ℓ = 0) and lowest at or near integer ℓ as predicted. Moreover, we observe that the Gaussian component still manifests at fractional ℓ; we believe this is due to the absence of vortices on the z-axis as described by Berry [J. Opt. A 6, 259 (2004)]. Our results have provided an alternative method to describe fractional vortex beams, as well as empirical validation for Berry's theoretical work on the fractional vortex beam.