Strongly Enhanced Raman Optical Activity of Chiral Molecules by Vector Exceptional Points

Raman optical activity (ROA) is a powerful spectroscopic technique for obtaining the detailed structural information of chiral molecular species. However, the widespread use of such a technique is limited by the weakness of small signal intensities. How to improve the detection efficiency of the ROA technique has become a key problem in recent years. Here, we propose a new scheme to realize the surface-enhanced ROA based on vector exceptional points (EPs). This type of EPs is realized by suitably tuning the coupling strength and radiation losses for a pair of orthogonal polarization modes in the dielectric photonic crystal slab. It is found that electric fields, magnetic fields, and their gradients can be significantly modified near the photonic crystal slab around the vector EPs, resulting in the enhancement of ROA signal by more than 3 orders of magnitude. Our finding provides a new way to tailor the ROA by designing dielectric structures without the influence of photothermal problems, which widely exist in the plasmonic systems.