Tailoring near-field heat transfer through inverse design and nonlinear media

Non-contact near-field energy transfer is an important process with ramifications to emerging applications in energy conversion. In this talk, we describe recent efforts aimed at enhancing and modifying radiative near field heat transfer (RHT) in nanostructured media. We present large-scale optimization techniques that can discover aperiodic multi-layered structures outperforming RHT in uniform media and which we also exploit to demonstrate complex 2d metallic structures (periodic gratings with complex surface topology) exhibiting some of the largest heat-transfer rates reported thus far. Finally, we describe a scheme which exploits the externally driven, intrinsic Kerr χ⁽³⁾ nonlinearity of III-V semiconductors and chalcogenides to upconvert thermal radiation from mid-infrared to near-infrared wavelengths. We employ this scheme in planar materials supporting surface polaritons to demonstrate significant near field heat transfer between materials of dissimilar resonance wavelengths and show that it can be exploited to achieve thermal refrigeration and tunable heat exchange (under arbitrary temperature differentials).