Polarization and coherence of light in nanostructures

• Applicant: Professor Dr. Klas Lindfors, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Experimental Condensed Matter Physics
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 324399575

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.

• DFG Programme: Research Grants