Institute Colloquium of Physics and Chemistry

On Tuesday, June 21, 2022, at 5:15 p.m. in the Faraday Lecture Hall, Dr. Chris Sturm University of Leipzig will speak on the topic:

„EXCEPTIONAL POINTS IN OPTICS: FROM BULK MATERIALS TO ONE DIMENSIONAL CONFINED SYSTEM”

Exceptional points (EP) arise in non-Hermitian systems by a degeneration of the complex-valued eigenvalues and eigenstates and have raised the interest of the scientific community in the last years. On the one hand they are interesting for optical devices and sensing application and on the other hand the investigations are driven by the search of topological nontrivial systems. The research on EP was initiated by W. Voigt. In 1902 he discovered that for certain directions in orthorhombic crystals only one circular polarized eigenstate exists, as soon as the absorption sets in, which corresponds to an EP in the momentum space. The presence of such EP is not limited to orthorhombic crystals only and appears in many optical systems. Here we present an overview of the appearance and the properties of these EPs in bulk crystal and optically one-dimensional confined systems. We show that the properties of the EPs in bulk crystals are determined by the symmetry of the system, which allows to distinguish between optically biaxial materials having triclinic, monoclinic or orthorhombic crystal symmetry. In the case of an optical confinement, EPs can even appear in systems consisting of optically uniaxial materials, like thin films or microresonators, which were recently observed experimentally. Furthermore, in contrast to bulk crystals, the properties of the EPs are determined not only by the material properties but also by the design, e.g., film thickness and confinement properties, of the system.