Whole LWIR Directional Thermal Emission Based on ENZ Thin Films

Abstract

Abstract Long‐wave infrared (LWIR) of 8–14 μm is an imperative atmospheric transmission window for applications such as infrared detectors, radiative cooling, and infrared stealth. Attempts to manipulate thermal emission in the LWIR band consist of either directional emission but narrowband or LWIR emission but non‐directional. Directional thermal emission covering the entire LWIR band has remained elusive, so far. Here, a whole LWIR directional thermal emitter is introduced consisting of top epsilon‐near‐zero (ENZ) films (SiO 2 /SiO/Al 2 O 3 ), a dielectric gap (Ge), and bottom ENZ films (TiO 2 /Ta 2 O 5 ) on a metal. The emitter exhibits high emissivity (>0.9) in p‐polarization at specific directions (72°–82°) covering the entire 8–14 μm atmospheric window. Additionally, infrared encryption information on the emitter can only be observed in p‐polarization in the oblique direction. This approach introduces a new route toward simultaneous control of bandwidth and directionality of thermal emission and has inclusive applications such as infrared camouflage and energy management.