Abstracts Book - IMRC 2018

• SC6-O017 Invited Talk
FREQUENCY-SELECTIVE NEAR-FIELD RADIATIVE HEAT TRANSFER
ENHANCEMENT VIA INVERSE DESIGN
Alejandro Rodriguez 1 , Weiliang Jin 1 , Sean Molesky 1 , Zin Lin 2
1 Princeton University, Electrical Engineering, United States. 2 Harvard University, SEAS, United
States.
The super-Planckian features of radiative heat transfer in the near-field are
known to depend strongly on both material and geometric properties. However,
the relative importance and interplay of these two facets, and the degree to
which they can be used to enhance heat transfer, remains an open
question. Typical low-loss materials do not support polariton resonances at the
required wavelengths, and often lack sufficient thermal stability to withstand
longterm operation at the required temperatures. Furthermore, even in
situations where polaritonic resonances exist, planar designs fall well short of
achievable rates dictated by energy conservation. In this talk, we provide a highlevel
view of recent theoretical works aimed at enhancing heat transfer and of its
ultimate limitations in structured media. We show that
unconventional geometries discovered by inverse design (large-scale
optimization) can lead to flux rates that are orders of magnitude larger than can
be achieved with unstructured media. First, we explore structures optimized
over only one dimension—multilayer slabs that demonstrate perfect rate
matching over a much broader range of evanescent wavevectors. Second, we
consider two-dimensional grating geometries, focusing on RHT between
different configurations of tungsten (W) and iron (Fe) materials at infrared
wavelengths far the planar surface resonance condition. We discover grating
geometries that selectively achieve 80% (30%) of the transfer rate corresponding
to a pair of ideal lossless metal plates supporting surface polaritons.
Such optimized gratings are found to decrease the effective material dissipation
rate via careful tuning of the scattering between bulk resonances, achieving
~100 times enhancement in lossy metallic gratings. More interestingly, we find
that while the resulting RHT enhancements fall short of the bounds set by
energy conservation, but nevertheles follow the predicted scaling with material
properties (susceptibility χ).