Narrowband and spectrally robust thermal emission from metallic thin films on top of epsilon-near-zero substrates

Abstract

The absorption and emission of infrared radiation by ultra-thin metallic films is a key element in several thermal engineering applications such as heat and energy management, and thermal camouflage. However, ultra-thin metallic films are broadband and low-efficiency emitters. Here, we demonstrate numerically and experimentally that metallic films placed on top of epsilon-near-zero (ENZ) substrates become narrowband and efficient thermal emitters. Our experiments show that ENZ-based emitters feature a narrow linewidth whose frequency positioning is robust against variations in the geometry of the system and the observation angle. Moreover, since ENZ emitters are based on the material properties of the substrate, no nanofabrication processes are needed, opening the pathway towards widefield and large-scale applications.