Frontiers in Optical Materials
Teri Odom, Northwestern University
The ability to structure matter from very small (nanometers) to large (millimeters) length scales has enabled a wide variety of new materials with almost “science fiction”-like optical properties to emerge. This session consists of topics that focus on two different types of structures that can manipulate light in unexpected ways. The topics complement each other perfectly and highlight the breadth of new possibilities that can result by controlling structures at the right length scales. First, the approach to create new structures: top-down fabrication methods are used to produce metamaterials while bottom-up chemical syntheses are used to grow nanomaterials for solar cells. Second, the materials themselves: metamaterials rely on metals while nanostructured solar cells rely on ceramics and semiconductors. Finally, the wavelengths of light: the first metamaterials interacted with light at microwave frequencies (ca. one meter) while nanostructured photovoltaic devices interact with light at optical frequencies (several hundred nanometers).
Metamaterials have captured the imagination of people from a wide range of backgrounds and ages—from scientists and engineers who are interested in manipulating light to children and fans of Harry Potter and his invisibility cloak (author: J.K. Rowling). Of course the underlying motivation for this interest is quite different. Scientists want to know how structured materials can be designed to exhibit new and exceptional properties; others simply want to know when they will be able to purchase a garment that can render them invisible.
Metamaterials are constructed from composite (metal and dielectric) building blocks whose sizes are much smaller than the wavelength of incident light. The idea that such engineered materials could be “left-handed” or cause light to bend the “wrong” way through a material was first introduced in 1968. The first experimental
realization of this negative refractive index effect was demonstrated by D.R. Smith in 2000 at microwave frequencies. In this case, each building block in the artificial lattice had an overall size of several millimeters, and each was composed of wires and “split rings.” The two most intriguing applications of metamaterials include their use as “cloaking” devices to render objects invisible at will and as “super-lenses” to image
features much smaller than optical wavelengths.
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