arXiv 0901.38132009-01physics.optics

轨道angular momentum依赖于极化

Orbital angular momentum is dependent on polarization

Chun-Fang Li

备注：: This article has been withdrawn by the author for it is replaced with the article arXiv:0909.2306

摘要：

结果表明，自由电磁场的动量密度分裂为两部分。由于横截性条件，对净动量没有贡献。另一个产生所有的动力。前一部分产生的角动量是自旋，后一部分产生的角动量是轨道角动量。给出了自旋和轨道角动量在倒易空间中电矢量的表达式。以这种方式定义的自旋和轨道角动量用于研究最近发表的论文[Phys.Rev.A78，063831（2008）]中描述的非傍轴光束的角动量。发现轨道角动量除了依赖于$l$项外，还依赖于两个全局量，即用广义Jones矢量表示的极化和用单位矢量$\mathbf{I}$表示的新特征，而自旋只依赖于极化.讨论了$\mathbf{I}$效应对轨道角动量的偏振依赖性。文中还对所得结果作了一些应用。利用自旋起源于动量密度中对净动量没有贡献的部分这一事实，说明圆极化平面波的自旋不存在佯谬。自旋和轨道角动量的偏振依赖性被证明是起源的转换从近轴拉盖尔-高斯光束的自旋到轨道角动量的聚焦光束通过高数值孔径。

英文摘要：

It is shown that the momentum density of free electromagnetic field splits into two parts. One has no contribution to the net momentum due to the transversality condition. The other yields all the momentum. The angular momentum that originates from the former part is spin, and the angular momentum that originates from the latter part is orbital angular momentum. Expressions for the spin and orbital angular momentum are given in terms of the electric vector in reciprocal space. The spin and orbital angular momentum defined this way are used to investigate the angular momentum of nonparaxial beams that are described in a recently published paper [Phys. Rev. A 78, 063831 (2008)]. It is found that the orbital angular momentum depends, apart from an $l$-dependent term, on two global quantities, the polarization represented by a generalized Jones vector and a new characteristic represented by a unit vector $\mathbf{I}$, though the spin depends only on the polarization. The polarization dependence of orbital angular momentum through the effect of $\mathbf{I}$ is obtained and discussed. Some applications of the result obtained here are also made. The fact that the spin originates from the part of momentum density that has no contribution to the net momentum is used to show that there does not exist the paradox on the spin of circularly polarized plane wave. The polarization dependence of both spin and orbital angular momentum is shown to be the origin of conversion from the spin of a paraxial Laguerre-Gaussian beam into the orbital angular momentum of the focused beam through a high numerical aperture.

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摘要：

英文摘要：

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