Nanophotonic Approaches to Controlling Spectral and Directional Thermal Emission

Nanophotonic structures have shown great promise in controlling the spectral and directional nature of thermal emission. Yet thermal emission's intrinsically broadband and omnidirectional nature have posed a fundamental challenge in simultaneously controlling these characteristics. In this talk, we will present our theoretical, computational and experimental approaches to engineering the spectral and directional emissivity in fruitful ways. We will introduce a coupled-mode theory capable of describing highly complex emissivity from multi-resonant systems. We will also describe a tandem ResNet-based inverse design technique that allows for the design of highly complex supercell metasurfaces which exhibit tailored, multispectral emissivity responses. As an example of a system that can benefit from multiple spectral peaks, we will also describe a multi-scale Mie resonant architecture that is simultaneously ultralight and also has enhanced emissivity for novel aerospace applications. Beyond spectral control, we will next discuss our work on enabling anomalous directional control of emissivity over broad spectral bandwidths. In particular we will describe how gradient Epsilon-near-zero (ENZ) photonic structure can enable broadband directional thermal emission. We will also show experimental results on how gradient ENZ thermal emitters can be fabricated from both oxides as well as graded-doped III-V films, enabling new capabilities in the control of thermal emission.