Controllable symmetric and asymmetric spin splitting of Laguerre-Gaussian beams assisted by surface plasmon resonance.

The spin splitting of light beams carrying orbital angular momentum (OAM) is investigated theoretically in attenuated internal reflection in the Kretschmann configuration. The excitation of the surface plasmon resonance (SPR) can significantly enhance the OAM-induced Imbert-Fedorov (IF) shift and the OAM-dependent spin splitting. The cooperation effect of these two shifts will result in an asymmetric spin splitting, which varies with the incident angle and polarization state. Specially, at the SPR angle, the OAM-induced IF shift vanishes, and the OAM-dependent spin splitting will cause a symmetric spin splitting. However, when the incident beam is horizontally polarized, the OAM-induced IF shift predominates. Thus the two spin components of the reflected will not be split; instead, they will be shifted together. This flexible control of the optical spin splitting can find applications in quantum information and precision metrology.