利用轨道角动量操控光子自旋霍尔效应中的非对称自旋分裂

Steering Asymmetric Spin Splitting in Photonic Spin Hall Effect by Orbital Angular Momentum

基于平面波角谱理论研究了利用轨道角动量操控光子自旋霍尔效应中的非对称分裂。以光束在空气-玻璃界面反射为例,建立了描述涡旋光束的光子自旋霍尔效应的传输模型,发现左旋和右旋圆偏振分量的横向位移是关于入射面不对称的,其中两个自旋分量位移的大小和方向是由涡旋光束的拓扑荷数所决定。轨道角动量诱导的非对称分裂可以看成是两自旋分量相对于入射面的整体偏移,这个轨道偏移本质上可以看成是线偏振涡旋光束的伊姆伯特费多罗夫(Imbert-Fedorov)效应。这些现象的物理机制归结于界面处的自旋-轨道相互作用和轨道-轨道转换,且与高斯光束所对应的对称分裂略有不同。研究结果表明轨道角动量为操控光子自旋霍尔效应提供了一个可选择的自由度。

Based on the angular spectrum theory of plane wave, the orbital angular momentum steer asymmetric splitting in photonic spin Hall effect （SHE） is studied. Taking the beam reflection at an air-glass interface for example, a propagation model describing the SHE of vortex beam is established, which clearly shows that the transverse displacements of left-handed and right-handed circular polarization components are asymmetric with regard to the incident plane. Particularly, the displacement magnitudes and directions of the two spin components are significantly affected by the topological charge of vortex beam. The asymmetric splitting is steered by orbital angular momentum which can be regarded as integral transverse shifts of two spin components for the incident plane. The integral transverse shifts correspond to Imbert-Fedorov effects of linear polarization vortex beam. The physics nature of these phenomenon are attributable to the spin-orbit interaction and orbit-orbit conversion at the interface, and this is little different from its symmetric counterpart for Gauss beams. The results suggest that the orbital angular momentum of light provides an alternative degree of freedom for tuning the photonic SHE.