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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.


Windows as the Adaptive Skin of a Building

The energy expended to maintain comfortable indoor building climates is enormous, amounting to 30-40% of the world’s primary energy sources. This is particularly true in colder climates, as in Canada, which has some of the highest per capita costs for heating and cooling in the world. Glass windows are a major contributor to this high cost, as they are the weakest energy link in the building envelope. The solution is not to make windows smaller, since they provide desirable visual contact with the outdoors and it is widely believed that natural daylight is important for human well-being. Rather, the solution is to re-imagine windows as the adaptive skin of a building, acting in harmony with the light and heat provided by the sun.

The production of windows relies on intelligent use of materials. Given current progress in manipulating materials on very small scales, now is an excellent time in history to ask: what is the best window for human beings? Based on recent research initiatives, it is reasonable to expect that future windows will incorporate some or all of the following characteristics:

1. Optical switching: the ability to manipulate transparency on demand using color-changing electrochromic materials;
2. Enhanced day-lighting: the use of angularly selective materials and devices to eliminate glare and provide comfortable day-lighting throughout the day;
3. Intelligent response: the coordination of switchable glass panes to behave like the human skin, where different panes behave differently at the same time.

Dr. Chau aims to contribute to this evolving vision of windows by creating a multi-disciplinary consortium with expertise in nano-optics, nanofabrication, visual perception, optical physics, daylighting, electrochemistry, sustainable buildings, and behavioral psychology. The team will explore smart windows across different size scales and disciplines, ranging from the nano-scale science of light transport and electrochromic behavior to the nuanced relationships between windows, buildings, and their occupants.


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 researchers from the US, Brazil, and Slovenia 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.