Controlling Directionality of Infrared Radiation with Metamaterials

Thermal radiation is the property that all forms of matter have, due to the intrinsic vibrations as a result of their temperature. This has spurred the desire to study and use this ever-present phenomena. Controlling and detecting thermal radiation has relevance in modern-world applications, ranging from high temperature thermal barriers used on airplanes to protect the turbines from overheating to energy conversion devices being improved with advances in solar cell design.

Control over the thermal radiation is achieved through the understanding of what the desired properties will be and then designing a material system that can fulfill the users’ criteria. The criteria that can be controlled vary depending on application and can range from having a broadband polarized emission, to having selective narrowband circular polarized emission at specific angles. The more distinctive the properties, the more degrees of control are needed to accomplish it. We will introduce the concept of symmetries of material systems that, when broken, allow for additional degrees of freedom to control the thermal radiation. We will also discuss how we perform the measurements, to demonstrate the methods used to verify that our control of the thermal radiation was valid. A spin-polarized angle-resolved spectroscopy (SPARTES) setup is used for the measurements to substantiate the claim that we can design structures that control their wavelength, angles of emission and polarization properties.

Thermal metamaterials designs are a great interest in high temperature applications. We explore various structured material surfaces that maintain their selective angular emission properties even when raised to high temperatures. Using different structures and materials, it is clear that our thermal radiation can be engineered to elicit different spectral responses at selective angles.

To explore the limits of our control, we observe the photon spin characteristics of thermal radiation. In general, objects in nature have little to no spin angular momentum. However, we can engineer a symmetry-broken metasurface that demonstrates this generation of circular polarized thermal emission without the presence of magnetic fields with high selectivity. We focus here on the affect that symmetry has on the spin-dependent polarization properties and how symmetry is a good metric to focus on when controlling the temporal, spatial and spin coherence of thermal radiation.