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Plasmonic Metamaterials: Bridging Optics and the Nano-World

Dr. Chau is exploring new ways to manipulate light using metallic nanostructures either in one-dimensional (layers), two dimensional (wires), or three-dimensional (particles) configurations. Collectively, such structures are known as “plasmonic metamaterials”. These materials are “plasmonic” because they interact with light by conversion into surface plasmon polaritons (SPPs) – light waves bound to the surface of metals. They are “metamaterials” because they can possess macroscopic properties that appear to bend the conventional rules of optics. For example, a planar slab formed by a stack of metal and dielectric nano-layers can refract a light beam incident from air to the same side of the normal, effectively behaving like a slab with a negative index of refraction [Xu, Nature 2013]. This field of research is relatively new because the possibility of engineering optical materials from the ground up within a short time frame has become feasible only with recent developments in computational electromagnetics and nanofabrication. Dr. Chau is exploring how materials engineered in this way can be used for light-based applications such as imaging and optical sensors.


Radiation Pressure and Light Momentum

Consensus on a single electrodynamic theory has yet to be reached. Discord was seeded over a century ago when Abraham and Minkowski proposed different forms of electromagnetic momentum density and has since expanded in scope with the gradual introduction of other forms of momentum and force densities. Although degenerate sets of electrodynamic postulates can be fashioned to comply with global energy and momentum conservation, hope remains to isolate a single theory based on detailed comparison between force density predictions and radiation pressure experiments. This comparison is two-fold challenging because there are just a handful of quantitative radiation pressure measurements over the past century and the solutions developed from different postulates, which consist of approximate expressions and inferential deductions, are scattered throughout the literature.

To resolve this issue, Dr. Chau and his team have developed a simulation testbed that solves equations of fluid dynamics and electrodynamics to model various radiation pressure experiments conducted over the last century [Bethune-Waddell and Chau, Rep. Prog. Phys. 2015]. Dr. Chau is also working with an international team of researchers to develop highly sensitive techniques to measure the deflection of small objects under light action. Detailed comparisons between simulations and experiments should reveal a single theory of electrodynamics.