Structured coherent thermal emission from non-Hermitian metasurfaces.

Abstract

Metasurfaces can reshape thermal radiation with tailored directionality, spectral selectivity and polarization control, yet coherent thermal emission exhibiting vectorial polarization or structured light property has been rarely demonstrated. Here, we introduce a non-Hermitian thermal meta-emitter that experimentally generates highly directional, rainbow-free, vectorial-polarized thermal emission. Through perturbation-induced Brillouin-zone folding, we couple high-radiative-loss Fabry-Perót modes to symmetry-protected bound states in the continuum and exploit non-Hermitian dynamics near exceptional points to achieve simultaneous dispersion and loss engineering. This yields a sharp variation of the radiative Q-factor in k-space, flexibly triggering vectorial-polarized emissions only at selected output angles. Experimental studies reveal doughnut-shaped narrowband thermal emission in the 3-5 μm atmospheric transparency window, exhibiting high spectral purity, extreme directionality and distinct vectorial polarizations. Our design establishes a powerful non-Hermitian platform to sculpt incoherent thermal fluctuations into coherent vectorial-polarized beams at a specific frequency, overcoming trade-offs in coherence, spectral selectivity and polarization control.