Directional Thermal Emission Covering Two Atmospheric Windows

Abstract Controlling directional thermal emission to match the ultra‐broadband atmospheric window is a long‐standing scientific challenge. Here, a strategy is introduced for achieving ultra‐broadband directional thermal emission matching the atmospheric window by combining Fabry–Perot resonances and the Brewster effect. The planar system, comprising a thin dielectric film (Ge) on a radiative substrate, exhibits high p ‐polarized emissivity (> 0.9) at specific directions (76°–84°) covering the entire atmospheric window (3–5 and 8–14 µm) and high omnidirectional emission (> 0.7) in the non‐atmospheric window (5–8 µm) for simultaneous efficient radiative cooling. Moreover, it can integrate independent dual‐band (visible–IR) information encryption and the infrared information anti‐snooping function. The approach offers unique insights into controlling thermal emission using planar films, with broad implications in camouflage, thermal management, and encryption.