Subwavelength broadband light-harvesting metacoating for infrared camouflage and anti-counterfeiting empowered by inverse design

Abstract

Broadband mid-infrared (MIR) light harvesting is critical for a wide range of applications, including thermophotovoltaic conversion, thermal sensing and imaging, infrared camouflage and anti-counterfeiting technologies. In this study, we present the design and experimental validation of a deep-subwavelength broadband MIR light-harvesting metacoating (MMC), optimized through a genetic algorithm (GA)-based inverse design approach. The strength of this approach lies in its ability to automate and optimize the complex multilayer structure, encompassing both material selection and structural thickness, thereby achieving unparalleled performance in broadband MIR light absorption, with an average absorbance of approximately 0.85 across the 3–13 μm spectral range and nearly perfect absorption within the 4–12 μm range. This exceptional performance is attributed to strong electromagnetic localization within its multilayer configuration, facilitating efficient energy dissipation via high-loss materials such as bismuth and titanium. Notably, the MMC exhibits robust performance with respect to angle and polarization variations, maintaining high absorbance even at incident angles up to 70°. Its large-area fabrication capabilities and compatibility with various substrates further enhance its practical applicability. Two specific applications, long-wavelength infrared camouflage and anti-counterfeiting, highlight its potential for real-world deployment. In these applications, the MMC seamlessly integrates into high-emission environments and enables the modulation of patterned infrared emission, providing a lithography-free, cost-effective solution compared to conventional methods relying on artificially engineered structures. This work underscores the versatility of the developed MMC for a diverse array of MIR applications, ranging from camouflage technologies to advanced security measures.