Extreme Wave Manipulation via Non-Hermitian Metagratings on Degenerated States

Metagratings offer promising opportunities for highly efficient yet anomalous wave-diffraction control characterized by scattering matrices. In this work, those degenerated states of scattering matrices, arising from elaborately induced non-Hermiticity and encoding unique scattering behaviors, are of interest. In par-ticular, we theoretically and experimentally investigate the exotic degeneracies, exceptional points (EPs) and diabolic points (DPs) in such scattering systems. We show the distinct response strength induced by EP and DP. The extremely asymmetrical reflection occurs on the EP state in a metagrating, which exhibits a stronger reaction to disturbances and offers opportunities for microvariable detection and external per-turbation monitoring. As a contrast, a stable dual-angle absorber is proposed on the DP state, which is almost unaffected by external perturbations. Our work may pave the way for extreme wave manipulation via non-Hermitian metagratings on degenerated states.