A body exposed to sunlight can be cooled by thermal radiation if it emits strongly in the infrared while being highly reflective in the in the solar spectrum range. Thus, thermal radiation emitted by the body can reach outer space, leading to efficient cooling. This is the so-called daytime radiative cooling. This principle can be used for various applications such as thermal management of buildings to reduce energy consumption. the different approaches to obtain these coatings which cool completely passively will be presented.

We present our experimental demonstration of broadband directional thermal emission enabled by gradient epsilon-near-zero materials that can support leaky modes that couple to free-space waves at fixed angles of incidence over a broad bandwidth. We will also summarize some of our recent progress in radiative cooling, including superwhite, UV-reflective paints, and how selective thermal emitters can enable optimal radiative cooling for vertical facades that face both the ground and the sky.

Spatially coherent thermal emission can be engineered by integrating periodic structures into a material supporting surface phonon polaritons. Extending functionality to additional spatial directions or emission frequencies requires using more sophisticated photonic structures. In this talk I will discuss how superstructure gratings can be used to engineer additional spatially coherent modes into the emission of a grating. In particular, we will discuss both the choice of design, as well as the limitations associated with the partial spatial coherence of surface phonon polaritons.

We present a novel far-field approach to direct thermal radiation to realize spatially structured radiative cooling. By using geometrical optics, thermal energy can be transferred from a sample to a structured temperature landscape. Manipulating the thermal radiation incident on the sample, renders it possible to create a thermal pattern within the sample. We demonstrate the applicability of this novel approach of radiative cooling for structured and contactless temperature control in the laboratory by showing the possibility to induce thermal patterns and by radiative supercooling of a microfluidic sample.