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arXiv 1506.06016physics.optics
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光矩：电磁自旋和轨道角动量守恒定律及其意义

The optical torque: Electromagnetic spin and orbital angular momenta conservation laws and their significance

Manuel Nieto-Vesperinas

发表信息：
Physical Review A92, 043843 (2015)
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摘要：

在自旋和轨道角动量的基本守恒方程所涉及的物理导致新的法律和现象，我披露。为此，我分析了电磁波场的散射由一个小粒子，我假设偶极在广义上构成的正则系统。具体来说，在相当一般的条件下，这些定律可以帮助我们了解每个角动量对物体上的场施加的电磁扭矩的贡献和权重，该扭矩由消光和散射或反冲组成。部分。这导致了对它的效应的解释与迄今为止许多理论和实验工作所采用的解释不同，并且意味着反冲力矩的一部分抵消了通常被称为固有力矩的固有力矩，该固有力矩通常被认为是粒子自旋的原因。此外，我得到的贡献的空间结构的波，这个扭矩，未知的日期，显示其效果在轨道上的对象，并证明它往往会导致一个负扭矩的一个单一的粒子，即相反的入射螺旋，产生轨道运动相反，其自旋。此外，我建立了一个分解的电磁转矩到保守和非保守的组件，其中的螺旋度和它的流量发挥类似的作用，电磁力的能量和它的通量。我说明这些现象的例子梁，也显示了一些傍轴配方的领域不持有的横截性条件的困难。

英文摘要：

The physics involved in the fundamental conservation equations of the spin and orbital angular momenta leads to new laws and phenomena that I disclose. To this end, I analyse the scattering of an electromagnetic wavefield by the canonical system constituted by a small particle, which I assume dipolar in the wide sense. Specifically, under quite general conditions these laws lead to understanding how is the contribution and weight of each of those angular momenta to the electromagnetic torque exerted by the field on the object, which is shown to consist of an extinction and a scattering, or recoil, part. This leads to an interpretation of its effect different to that taken up till now by many theoretical and experimental works, and implies that a part of the recoil torque cancels the usually called intrinsic torque which was often considered responsible of the particle spinning. In addition, I obtain the contribution of the spatial structure of the wave to this torque, unknown to this date, showing its effect in the orbiting of the object, and demonstrating that it often leads to a negative torque on a single particle, i.e. opposite to the incident helicity, producing an orbital motion contrary to its spinning. Furthermore, I establish a decomposition of the electromagnetic torque into conservative and non-conservative components in which the helicity and its flow play a role analogous to the energy and its flux for electromagnetic forces. I illustrate these phenomena with examples of beams, also showing the difficulties of some paraxial formulations whose fields do not hold the transversality condition.

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