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近年来,国际上兴起了关于结构光场横自旋的研究热潮[1-4],并且与光的自旋霍尔效应[5-7]和拓扑光子学密切关联起来[8]。人们发现了结构光场横自旋在单向光接口技术中的潜在应用[9-12]。 其中,横自旋指的是垂直于结构光场运动方向的自旋角动量。按照标准的量子场论术语,它对应的是螺旋度为零的自旋状态。众所周知,电磁场作为无静止质量的矢量场,在自由真空中只有两个独立的横极化分量,其中左旋和右旋圆极化光分别描述螺旋度为±1的两种横光子,而螺旋度为零的纵光子和标光子可以用电磁场场强的纵极化分量来描述,对于辐射场而言它是不存在的(对于非辐射场而言,纵光子和标光子可以以虚光子的形式存在) 。由于这个原因,从一开始人们对结构光场的横自旋缺乏一个严格的物理图像,甚至对它有些神秘化,同时对它的某些物理性质存在一些误解。文献[1–2]的研究指出,横自旋与通常意义上的自旋不同,它不是量子化的。然而本文的研究表明,横自旋仍然是量子化的。
关于结构光场的横自旋研究,既有理论价值,也有实用价值。目前的研究已经将它与光子自旋的量子霍尔效应、拓扑光子学等领域密切关联起来。因此,我们有必要厘清横自旋的物理起源、弄清楚它的物理性质,为相关的理论与应用研究提供一个可靠的出发点。本文将以两种介质分界面处的表面波(隐失波)的横自旋为例,为结构光场横自旋建立一个严格的物理模型。
Investigations on Some Physical Properties of the Transverse Spin of Evanescent Waves
doi: 10.12178/1001-0548.2022404
- Received Date: 2022-11-25
- Rev Recd Date: 2023-02-10
- Available Online: 2023-10-08
- Publish Date: 2023-09-30
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Key words:
- angular momentum of light /
- evanescent waves /
- spinoptics /
- transverse spin
Abstract: In this paper we present some new investigations on the transverse spin of evanescent waves and obtain the following results: 1) the quantization form of the transverse spin is revealed; 2) from a unified point of view, the transverse spin can be attributed to the presence of an effective rest mass of evanescent waves; 3) the transverse spin can also be described by the spin matrix of the photon field; 4) unlike a free optical field in vacuum whose spin projection on the propagation direction is the only observable, owing to the effective rest mass, the spin projection of evanescent waves on other directions is also an observable, such that one can develop an optical analogy of spintronics, i.e., spinoptics.
Citation: | WANG Zhiyong, JIA Zhiguo, WANG Zhenwei, ZHENG Hongxiang, WANG Yixiang, DING Mingjuan, SHAO Guangcun, WANG Xiangru. Investigations on Some Physical Properties of the Transverse Spin of Evanescent Waves[J]. Journal of University of Electronic Science and Technology of China, 2023, 52(5): 675-680. doi: 10.12178/1001-0548.2022404 |