Abstract: Nanoscale photonic structures, by their small length scales, can manipulate light and heat in unprecedented ways, thereby enabling new technological possibilities for energy efficiency and generation. In this talk, I will show how nanophotonic structures can control the broadband electromagnetic fields associated with mid-infrared thermal radiation and sunlight to harness an unexploited thermodynamic resource – the cold of space – to improve the efficiency of terrestrial energy conversion systems.

I will present our body of work on radiative sky cooling, whereby sky-facing, thermal nanophotonic structures can passively cool themselves below their surroundings by emitting their heat as thermal radiation at wavelengths where Earth’s atmosphere is most transparent. I will show the first experimental demonstration of how this passive cooling effect can persist during the day under sunlight and show that, with selective thermal emitters and improved thermal engineering, a world record of 45°C below ambient can be achieved. I will also introduce two examples of how this passive cooling approach can improve the efficiency of energy conversion processes: in solar cells, and vapor-compression cycles. Theoretical frameworks will concurrently be introduced that allow us to rigorously understand the broadband electromagnetic response of nanophotonic structures, and the fundamental limits of their performance, for the absorption and emission of light and heat.

Finally, I will highlight new fundamental and applied research directions for controlling light and thermal radiation, particularly at mid-infrared wavelengths. We now have the remarkable opportunity to tackle important energy and environmental challenges by better controlling the radiative heat transfer happening around us everyday.

Biosketch: Aaswath Raman is Assistant Professor of Electrical and Systems Engineering at the University of Pennsylvania. His research interests include nanophotonics, metamaterials and plasmonic systems, thermal sciences, heat transfer, energy systems, and machine learning. He is also Co-Founder and Chief Scientific Officer of SkyCool Systems, a startup commercializing technology related to radiative sky cooling that he originally developed as a Research Associate at Stanford University beginning in 2013.

Aaswath received his Ph.D. in Applied Physics from Stanford University in 2013, and his A.B. in Physics and Astronomy, and M.S. in Computer Science from Harvard University in 2006. Prior to obtaining his Ph.D. he was a Program Manager at Microsoft. He is the recipient of the Sir James Lougheed Award of Distinction from the Government of Alberta, Canada, the SPIE Green Photonics Award for his work on solar cell light trapping and the Stanford Postdoctoral Research Award. In recognition of his work on radiative sky cooling, in 2015 Aaswath was named one of MIT Technology Review’s Innovators Under 35 (TR35).