Figure 3. Instability of a higher-order V-point in VVB with η = 2 generated by a q-plate with q = 1 and α₀ = 2.1 rad, acting on a TEM_0,0 vertically polarized beam.

(a) We plot the orientation angle ψ of the measured polarization ellipses, and the corresponding theoretical predictions, when varying δ between δ = π and δ = 3π/4 with steps of π/16. Simulations show that the original V-point splits into two pairs of C-points; similarly to the previous case, in each pair the two singularities have opposite handedness. In the experimental data, the formation of these two pairs can be observed clearly: as discussed in the main text, this is associated with the decay of the high-order phase vortex in each of the two circular components. Nevertheless, for each pair the system spatial resolution does not allow to distinguish two different C-points, because they remain very close to each other, at least for small deviations from the ideal case. In (b), we show the corresponding experimental and theoretical polarization patterns associated with these fields. Here, red and blue colored ellipses are associated with left (s₃ > 1) and right handed (s₃ < 1) polarization states, respectively.