Zhang Xiaohe, Shen Bo, Zhu Zhuqing, Rui Guanghao, He Jun, Cui Yiping, Gu Bing
Opt Express. 2022 Feb 14;30(4):5121-5130. doi: 10.1364/OE.449583.
Spin angular momentum (SAM) is widely used in spin-dependent unidirectional optical interfaces, optical manipulation, integrated optical signal processing, laser structuring and other fields, but its physical mechanism has not been fully understood so far. In this work, we investigate the three-dimensional (3D) SAM in tightly focused x-polarized first-order vortex beams from the perspectives of light field itself, phase distribution, and focusing propagation. It is shown that the distribution of three orthogonal components of SAM at the focal plane has pseudo two-fold rotational symmetry, because the cycloidal rotation of the electric field of the tightly focused vortex beam is opposite. The 3D SAM distribution in the focal region is visualized by mapping the 3D distribution of state of polarization (SoP). In addition, a principle experimental method for identifying the transverse SAM by using the direction of particle's rotation axis in optical tweezers is proposed.
自旋角动量（SAM）在自旋相关的单向光学界面、光学操控、集成光信号处理、激光微纳加工等领域有着广泛应用，但其物理机制至今尚未完全明晰。在本工作中，我们从光场本身、相位分布以及聚焦传播等角度，研究了紧聚焦x偏振一阶涡旋光束中的三维（3D）SAM。结果表明，由于紧聚焦涡旋光束电场的摆线旋转方向相反，SAM在焦平面上三个正交分量的分布具有伪二重旋转对称性。通过绘制偏振态（SoP）的三维分布，直观呈现了焦区内的3D SAM分布。此外，还提出了一种利用光镊中粒子旋转轴方向来识别横向SAM的原理性实验方法。
