近场高阶庞加莱球上拉盖尔-高斯光束的自旋-轨道耦合

Spin-Orbit Coupling of Laguerre-Gaussian Beams on High-Order Poincaré Sphere in Near Field

对非傍轴条件下光学角动量及自旋-轨道耦合的研究有助于人们认识亚波长结构中的光现象,近场中的倏逝波也可能产生强烈的自旋-轨道耦合。基于角谱衍射理论和Parseval定理,详细分析了高阶庞加莱球上拉盖尔-高斯矢量涡旋光束的传播波、倏逝波和角动量的近场演化特性以及倏逝波引起的自旋-轨道耦合。结果表明,在亚波长束腰宽度光束的源平面附近倏逝波作用强烈,在总光场中占主导地位。此外,近场中的轨道角动量同时包含横向电场和纵向电场的贡献,倏逝波中横向自旋角动量和横向偏振态相关,且存在自旋方向锁定现象。该研究为矢量涡旋光束在亚波长结构中的研究和应用提供了理论依据。

The research of optical angular momentum and spin-orbit coupling under non-paraxial conditions will help people understand the phenomenon of light in sub-wavelength structures.The evanescent wave in the near field may produce strong spin-orbit coupling.In this paper,based on the angle spectrum diffraction theory and Parseval theorem,the near field evolution characteristics of propagating waves,evanescent waves and angular momentum of Laguerre-Gaussian vector vortex beams on high-order Poincaré sphere are analyzed in detail,as well as the spin-orbit coupling caused by evanescent waves.The results show that the evanescent wave action near the source plane of the beam with sub-wavelength waist width is strong,and dominates the total optical field.Moreover,the orbital angular momentum contains the contributions of both the transverse and longitudinal electric fields in the near field,and the transverse spin angular momentum in the evanescent wave is related to the transverse polarization state,furthermore there is a phenomenon of spin direction locking.The research provides a theoretical support for the study and application of vector vortex beams in sub-wavelength structures.