Polarization and coherence of light in nanostructures

光的相干性在基础科学和技术中都起着重要的作用。光相干表现为电场分量之间的相关性。一个时空点场分量之间的相关性描述了光的偏振特性，偏振应被视为一个统计学概念，必须与时空相干性同等对待，而时空相干性与两个时空位置场分量之间的相关性有关。光的偏振在各种各样的光学现象中都很重要，从透射、反射和散射到场景的偏振成像和原子和分子跃迁的量子力学选择规则。直到最近，光偏振的研究还局限于近轴电磁场。随着纳米光学和等离子体动力学的出现，纳米结构的光场本质上是三维的，已经成为一个高度热门的研究领域。亚波长结构中的光场与自由空间中的光场的关键区别在于它们的三维性质。三维电磁场相干理论是近年来理论研究的热点之一。然而，尽管有令人兴奋的理论预测，如异常短和长相干长度，偏振和相干热辐射，以及光的安德森定位和光场矢量性质的依赖，但迄今为止，对纳米结构中光的统计特性的实验研究还很少。在本项目中，我们将开发扫描探针光学偏振法来表征三维光场的偏振特性，并将其应用于光学，特别是等离子体纳米结构的研究。计划研究的目标是：首次展示以亚波长空间分辨率绘制光的全三维偏振特性的可能性，探索部分相干光如何激发简单孤立等离子体结构（如等离子体纳米天线）的模式，以及研究超表面上光场的相干特性。这些目标的实现将导致纳米光学领域的重大进展，并将导致高影响力的出版物。该项目的一些科学问题和里程碑是论证光的三维相干矩阵的首次测量，探索部分偏光紧密聚焦光的相干特性的三维拓扑结构，以及研究相干矩阵在超表面上的空间分布以及是否存在局部相干度高的相干热点。该项目有可能在纳米光学领域开辟一个新的研究领域，并研究迄今为止尚未开发的光学领域。

The coherence properties of light play an important role in both fundamental science and technology. Optical coherence is manifested in correlations between electric field components. Correlations between field components at one space-time point describe the polarization properties of light and polarization should be viewed as a statistical concept that has to be handled on equal footing as temporal and spatial coherence, which are related to correlations between field components at two space-time positions. The polarization of light is important in a great variety of optical phenomena, ranging from transmission, reflection and scattering to polarimetric imaging of scenes and quantum-mechanical selection rules of atomic and molecular transitions. Until recently studies of optical polarization have been restricted to paraxial electromagnetic fields. With the emergence of nano-optics and plasmonics, nanostructures, around which optical fields are inherently three-dimensional (3D), have become a highly topical area of study. The critical difference between optical fields in sub-wavelength structures and in free-space is their 3D nature. The theory of coherence for 3D electromagnetic fields has been one of the key topics of theoretical research during the last few years. However, despite exciting theoretical predictions such as anomalously short and long coherence lengths, polarized and coherent thermal radiation, and the dependence of Anderson localization of light on the vectorial nature of optical fields, experimental studies on the statistical properties of light in nanostructures have been so far rare. In the proposed project we will develop scanning probe optical polarimetry to characterize the polarization properties of three-dimensional optical fields and apply it to study optical, in particular plasmonic nanostructures. The goals of the planned research are: to demonstrate the possibility to map the full 3D polarization properties of light with sub-wavelength spatial resolution for the first time, to explore how partially coherent light excites the modes of simple isolated plasmonic structures such as plasmonic nanoantennas, and to study the coherence properties of optical fields on metasurfaces. The accomplishment of these goals will lead to significant advances in the field of nano-optics and will result in high-impact publications. Some of the scientific questions and milestones of the project are to demonstrate the first measurement of the 3D coherence matrix of light, to explore the 3D topology of the coherence properties of partially polarized tightly focused light, and to study what is the spatial distribution of the coherence matrix on metasurfaces and whether there are coherence hot-spots where the degree of coherence is locally high. The project has the potential to open a new area of research in the field of nano-optics and to study so far unexplored aspects of optical fields.