Ornigotti Marco, Aiello Andrea
Opt Express. 2014 Mar 24;22(6):6586-96. doi: 10.1364/OE.22.006586.
Traditionally, the angular momentum of light is calculated for "bullet-like" electromagnetic wave packets, although in actual optical experiments "pencil-like" beams of light are more commonly used. The fact that a wave packet is bounded transversely and longitudinally while a beam has, in principle, an infinite extent along the direction of propagation, renders incomplete the textbook calculation of the spin/orbital separation of the angular momentum of a light beam. In this work we demonstrate that a novel, extra surface part must be added in order to preserve the gauge invariance of the optical angular momentum per unit length. The impact of this extra term is quantified by means of two examples: a Laguerre-Gaussian and a Bessel beam, both circularly polarized.
传统上，光的角动量是针对“子弹状”电磁波包计算的，尽管在实际光学实验中更常用的是“铅笔状”光束。波包在横向和纵向都是有界的，而光束原则上在传播方向上具有无限的范围，这使得教科书中关于光束角动量的自旋/轨道分离的计算并不完整。在这项工作中，我们证明必须添加一个新的额外表面部分，以保持每单位长度光学角动量的规范不变性。通过两个例子对这个额外项的影响进行了量化：一个拉盖尔 - 高斯光束和一个贝塞尔光束，两者均为圆偏振。
