Analysis of practical fractional vortex beams at far field

The subject of calculating the topological charge (TC) or vortex strength of optical vortices has generated divided opinions among scientists. This is due to the fact that proper analytical results are hard to support from the experimental point of view, leading to different results and conclusions. In this work we will present numerical data that shows the limits of TC measurements for practical fractional vortices and the possible challenges that high order measurements may pose. By analyzing the far field phase and the behavior of the transitions we have shown that they follow specific curves that depend not only on the TC but also on the beam waist. This leads us to present a new “strength staircase” for practical vortices. Our aim is to give some insight in practical scenarios that have not been taken into account in previous results. •Practical Fractional Vortex beams transition dynamics are studied and quantified.•The vortex strength staircase is obtained for practical vortices.•Utilization of a finite extension of the beam causes staircase non-uniformities.•The topological charge (TC) measured values depend not only on the initial TC but on the beam waist.