Photonic spin Hall effect by anisotropy-induced polarization gradient in momentum space

We demonstrate theoretically and experimentally a novel photonic spin Hall effect (PSHE), to the best of our knowledge, at an interface between air and uniaxial crystal, whose optical axis is within the interface plane. Owing to the anisotropy of the crystal, partial cross polarization conversion occurs. For a horizontally polarized paraxial Gaussian beam incidence, a linear polarization gradient forms along the in-plane wavevector in the reflected beam, allowing us to achieve spin separation in real space. The spin separation of the reflected beam can be tuned by rotating the optical axis of the crystal. A maximum spin-dependent displacement up to 0.45 times the incident beam waist is obtained at Brewster incidence. This novel anisotropy-induced PSHE deepens the understanding of spin–orbit interaction and provides a new way for control of spin photons.