Design at the Nanoscale: Reaching the Limits of Light-Matter Interactions
Owen Miller, Yale
Nanoscience is developing at a rapid pace, with ever more materials, form factors, and structural degrees of freedom now available. To confront these large design spaces, and leverage them for transformative technologies, new theoretical tools are needed. Across a range of photonics applications, I will demonstrate that the combination of large-scale computational optimization with new analytical frameworks enables rapid identification of superior designs, and spurs discovery of fundamental limits to wave-matter interactions. 
In photovoltaics, the famous ray-optical 4n^2 limit to absorption enhancement has for decades served as a critical design goal. I will show that at subwavelength scales, non-intuitive, computationally designed textures outperform random ones, and can closely approach 4n^2 enhancements. Pivoting to metallic structures, where there has not been an analogous “4n^2” limit, I will show how passivity imposes convex constraints on electromagnetic scattering, leading to fundamental limits to optical response in absorptive systems. The limits were stimulated by a computational discovery in nanoparticle optimization, where I will present theoretical designs and experimental measurements (by a collaborator) approaching upper bounds for absorption and scattering. The energy-conservation principles can be extended to the field of thermal radiation, where they generalize the ray-optical concept of a "blackbody" to near-field radiative heat transfer.