Chirality and angular momentum in optical radiation
Chirality and angular momentum in optical radiation
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DOI：
10.1103/physreva.85.063810
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发表时间：
2012-06-11
影响因子：
2.9
通讯作者：
Andrews, David L.
中科院分区：
文献类型：
--
作者：
Coles, Matt M.;Andrews, David L.
这篇论文用精确的量子电动力学术语发展了“光学手性密度”的光子属性，这是长期以来被认为是真空电磁场守恒量的几个度量之一。这一分析有助于理解最近对手性实验的一些解释，在这些实验中，这种测量和相关的手性通量被视为代表物理上独特的“超手性”现象。在完全量子化的形式中，手性密度被提升为算符状态，它对任意偏振基的探索揭示了与光学角动量和螺旋度算符的关系。分析具有复杂波前结构的多模光束，特别是拉盖尔-高斯模，可以更深入地理解光学手征性和光学角动量之间的相互作用。通过对光的光子特性的适当认识来发展理论，我们发现只有光的自旋角动量参与了这样的观测。此外，研究还表明，手征电磁辐射螺旋度的这些重要测量具有一个共同的基础，即与相反符号角动量相关的光学模群之间的差异。以圆二向色性速率的计算为例，用相干态模拟电磁场，发现有两个项对微分效应有贡献。主要贡献与左右手光子布居的差异有关；唯一的另一个贡献与量子光子数-位相不确定关系有关，它表现出与节点增强主张对应的正弦距离依赖关系。从全面的分析来看，“超手性”一词似乎可以被认为是多余的。
This paper develops, in precise quantum electrodynamic terms, photonic attributes of the "optical chirality density," one of several measures long known to be conserved quantities for a vacuum electromagnetic field. The analysis lends insights into some recent interpretations of chiroptical experiments, in which this measure, and an associated chirality flux, have been treated as representing physically distinctive "superchiral" phenomena. In the fully quantized formalism the chirality density is promoted to operator status, whose exploration with reference to an arbitrary polarization basis reveals relationships to optical angular momentum and helicity operators. Analyzing multimode beams with complex wave-front structures, notably Laguerre-Gaussian modes, affords a deeper understanding of the interplay between optical chirality and optical angular momentum. By developing theory with due cognizance of the photonic character of light, it emerges that only the spin-angular momentum of light is engaged in such observations. Furthermore, it is shown that these prominent measures of the helicity of chiral electromagnetic radiation have a common basis in differences between the populations of optical modes associated with angular momenta of opposite sign. Using a calculation of the rate of circular dichroism as an example, with coherent states to model the electromagnetic field, it is discovered that two terms contribute to the differential effect. The primary contribution relates to the difference in left- and right-handed photon populations; the only other contribution, which displays a sinusoidal distance dependence corresponding to the claim of nodal enhancements, is connected with the quantum photon number-phase uncertainty relation. From the full analysis, it appears that the term "superchiral" can be considered redundant.