Spin–orbit coupling mediated transverse spin mode rotation in a uniaxial crystal

Abstract

We demonstrate topological features in a spin–orbit coupled inhomogeneously polarized beam of light due to propagation of a linearly polarized focused Gaussian beam through a tilted–rotated (θ–ϕ) quartz crystal plate. The crystal plate is kept in a polarization interferometer, and transverse and longitudinal phase difference is introduced between the o- and e-wave-beams via (θ–ϕ) variation. The curvature in the phase difference, originating at a phase saddle, at the stem of an intensity forklet pattern, enables continuous rotation of the output two-lobe intensity pattern as a function of (θ–ϕ). The transverse spin-shift of the rotating output beam shows variation in both magnitude and slope. Such a study of exploring topological features arising due to spin–orbit coupling in simple optical systems is of fundamental interest and is expected to open up potential applications in the investigation of material anisotropy and polarization-sensitive sensing.