Fig. 6: Experimental validation of the T-spin and spin-momentum locking in a focused circularly polarized beam (CPB).
From: Dynamical and topological properties of the spin angular momenta in general electromagnetic fields
a–c Theoretically calculated y-, z-, and x-components, respectively, of the SAM densities of a focused LCP beam. d–f Corresponding experimental results. The corresponding theoretical and experimental results for the focused RCP beam can be found detailly in Supplementary Fig. 8 and Fig. 10. The optical axis is along the x-direction. Since the incident beam is changed from LCP to RCP, the y- and z-components of the SAM remain unchanged, thereby manifesting a helicity-independent T-spin. In contrast, the sign of the x-component of the SAM changes from positive to negative. This spin component contains two parts: the L-spin and the helicity-dependent T-spin. Together with the inverted propagating property, the T-spin of the focused circularly polarized light was demonstrated to possess ℤ4 topological invariance, which matches well with the theoretical analysis.
