Figure 4: Experimental observation of vortex generation by initial excitation of two Dirac points.
From: Unveiling pseudospin and angular momentum in photonic graphene
(a) The input intensity pattern and k-space spectrum of the probe beam from two-beam interference, and (e) its output spectrum. Notice the new spectral component appearing at the third Dirac point due to Bragg reflection. (b,f) Output far-field intensity patterns generated at the third Dirac point when only sublattice A (top row) or B (bottom row) is excited. The insets illustrate the selective excitation of two sublattices by the probe beam. (c,g) Opposite vortex singularities observed from the interferograms of b and f. (d,h) Output phase structure obtained from corresponding numerical simulation, where the opposite singularities are illustrated by the white arrows.
