Angle-Resolved Thermal Emission Spectroscopy Characterization of Non-Hermitian Metacrystals

We establish angle-resolved thermal emission spectroscopy as an alternative platform to characterize the intrinsic eigenmode properties of non-Hermitian systems. This method can directly map the dispersion of metacrystals within the light cone with high angular resolution. To illustrate its usefulness, we demonstrate the existence of bound states in the continuum (BICs) and non-Hermitian Fermi arcs in a planar corrugated metacrystal by measuring its angle-resolved thermal emission spectra. We show that a change in the thickness of the metacrystal can induce a band inversion between a BIC and a radiative state, and a pair of exceptional points emerge when the band inversion occurs. With this approach, the band mapping of non-Hermitian photonic systems can become a relatively straightforward task.