A study of zeros in optical fields and the origins of spin in wave fields

光场零点和波场自旋起源的研究

• 批准号: 2444407
• 金额: --
• 依托单位: King's College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2444407
• 关键词: study; zeros; optical; fields; origins

When lots of plane waves interfere, it is possible for point-like nodes to exist in the interference pattern. By point-like nodes we mean zeros in the electric field, confined in all three dimensions, so that the intensity of the field rises in all outward directions. Just like in the centre of a doughnut beam, the canonical momentum (provided by the electric field) vanishes in a 3D electric field zero, creating a vortex-like circulation of momentum. A traditional vortex in a doughnut beam is two dimensional and can be characterised by the winding of the phase of the transverse field components. 3D zeros are largely unstudied - it is not known how polarisation singularities (C/L-lines which are continuous and should pass through the zero in some way) are arranged by the 3D zero, and there is no formal way to characterise the different types of 3D zero that exist - we are trying to provide answers to these statements. In far-field radiation, zeros can impart non-diffractive properties into the nearby field.Light carries intrinsic spin angular momentum (SAM) when the electric or magnetic field vector rotates over time. Using Maxwell's equations, this vector equation can be decomposed into a sum of two distinct terms, akin to the well-known Poynting vector decomposition into orbital and spin currents. We present the first general study of this spin decomposition, showing that the two terms, which we call canonical and Poynting spin, are chiral analogies to the canonical and spin momenta of light in its interaction with matter. Both canonical and Poynting spin incorporate spatial variation of the electric and magnetic fields and are influenced by optical orbital angular momentum (OAM). The decomposition allows us to show that the OAM of a linearly polarised vortex beam can impart a first-order preferential force to chiral matter in the absence of spin.

当大量平面波干涉时，干涉图中可能存在点状节点。我们所说的点状节点是指电场中的零点，被限制在所有三个维度中，因此电场的强度在所有向外方向上都上升。就像在甜甜圈光束的中心一样，规范动量（由电场提供）在三维电场中消失为零，产生了类似漩涡的动量循环。传统的环形束涡旋是二维的，可以通过横向场分量的相位缠绕来表征。3D零点在很大程度上是未被研究的——我们不知道偏振奇点（C/ l线是连续的，应该以某种方式通过零点）是如何由3D零点排列的，也没有正式的方法来描述存在的不同类型的3D零点——我们正试图为这些陈述提供答案。在远场辐射中，零可以将非衍射特性传递到近场。当电场或磁场矢量随时间旋转时，光携带本征自旋角动量（SAM）。使用麦克斯韦方程，这个矢量方程可以分解成两个不同项的和，类似于著名的波印廷矢量分解成轨道和自旋电流。我们提出了这种自旋分解的第一个一般研究，表明这两个术语，我们称之为正则自旋和坡印廷自旋，是光与物质相互作用中的正则自旋动量和自旋动量的手性类比。正则自旋和坡印亭自旋都包含了电场和磁场的空间变化，并受到光轨道角动量（OAM）的影响。分解使我们能够证明，在没有自旋的情况下，线性极化涡旋光束的OAM可以赋予手性物质一阶优先力。