Measuring the topological charge of a vortex beam via the self-rotating beam phase

We proposed a method to measure the topological charge of a vortex beam by using the self-rotating beam phase in this Letter. We investigated the far-field intensity patterns of the vortex beams passing through a phase hologram of the self-rotating beam with n = +2 theoretically and experimentally. The results demonstrate that the far-field intensity patterns cannot exhibit bright stripes when the topological charge of the vortex is positive (i.e., n ⋅ l > 0) and the calculated ratio relationship ξ can be used to identify the topological charge of the vortex beam. Differently, it can be found that the far-field intensity patterns exhibit several bright stripes when the topological charge of the vortex is negative (i.e., n ⋅ l < 0) and the number N of the bright stripes is equal to |l|−1(l represents the topological charge of the vortex beam). The experimental results are in good agreement with the theoretical ones. This method may inspire further research in the field of self-rotating beams.