On the natures of the spin and orbital parts of optical angular momentum
On the natures of the spin and orbital parts of optical angular momentum
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DOI：
10.1088/2040-8978/18/6/064004
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发表时间：
2016-06-01
影响因子：
2.1
通讯作者：
Yao, Alison M.
中科院分区：
文献类型：
--
作者：
Barnett, Stephen M.;Allen, L.;Yao, Alison M.
光学角动量的现代领域开始于艾伦等人在1992年的认识，即除了与偏振相关的自旋之外，具有螺旋相位前沿的光束还携带轨道角动量。然而，围绕着场的复杂性，特别是将角动量分离成自旋和轨道部分，存在着许多混乱和争论。在这里，我们借此机会陈述我们所理解的当前立场，我们提出了六个观点：（一）我们开始与1992年的论文，其中指出，拉盖尔-高斯模式，熟悉的激光物理，携带轨道角动量的重演。(ii)总的角动量可以分为自旋和轨道部分，但单独的两个部分都不是真正的角动量。(iii)自旋和轨道部分，虽然本身不是真正的角动量，但它们是不同的，并且有物理意义，这在一系列实验中已经得到了清楚的证明。(iv)在光束传播方向上的角动量的轨道部分不仅仅是线性动量的方位角分量。(v)自旋在传播方向上的分量不是螺旋度，尽管它们是相关的量。(vi)最后，角动量的自旋和轨道部分对应于自由电磁场的不同对称性，因此是独立的守恒量。
The modern field of optical angular momentum began with the realisation by Allen et al in 1992 that, in addition to the spin associated with polarisation, light beams with helical phase fronts carry orbital angular momentum. There has been much confusion and debate, however, surrounding the intricacies of the field and, in particular, the separation of the angular momentum into its spin and orbital parts. Here we take the opportunity to state the current position as we understand it, which we present as six perspectives: (i) we start with a reprise of the 1992 paper in which it was pointed out that the Laguerre-Gaussian modes, familiar from laser physics, carry orbital angular momentum. (ii) The total angular momentum may be separated into spin and orbital parts, but neither alone is a true angular momentum. (iii) The spin and orbital parts, although not themselves true angular momenta, are distinct and physically meaningful, as has been demonstrated clearly in a range of experiments. (iv) The orbital part of the angular momentum in the direction of propagation of a beam is not simply the azimuthal component of the linear momentum. (v) The component of spin in the direction of propagation is not the helicity, although these are related quantities. (vi) Finally, the spin and orbital parts of the angular momentum correspond to distinct symmetries of the free electromagnetic field and hence are separately conserved quantities.