Thursday, March 4, 2010

Background in Plasmonics

Nano-photonics is a field of science and technology that aims to manipulate light with equally miniscule structures in the same way that computer chips are used to route and switch electrical signals. Advanced computer simulations can now accurately describe the behavior of light as it interacts with such nanoscale structures that are more than a 1000 times smaller than a human hair or the glass telecom fibers that currently enable communication between people and computers anywhere in the world. Until recently it was a generally held belief that manipulation of light was limited to the relatively large wavelength scale of about 1 micrometer (0.001 millimeter) by the fundamental laws of diffraction. However, recent developments in the rapidly developing field of plasmonics have demonstrated that light can be controlled at much smaller length-scales (well below the wavelength or diffraction limit of light) by using metallic nanostructures. These metal structures are called plasmonic components.

The fact that light interacts strongly with metals has been observed for a very long time. The rich colors of stained glass windows and ancient glass artifacts result from the unique way light behaves when it encounters the minute metal structures in the glass; it generates little oscillation electrical currents inside the metal, known as plasmons (hence the name plasmonics). Only in the last two decades, have scientists obtained a deep understanding of the optical behavior of metal nanostructures and are able to use this knowledge to engineer unique metal particle shapes and arrays to attain a desired optical response.

It is important to understand that the concept of “light” is merely our perception of the visible portion of the electromagnetic spectrum. Humans perceive light as a wide range of colors (wavelengths) that can be produced by absorption, reflection, and scattering as light passes through different media (i.e. air, water, glass, semiconductors and metals). Similarly we recognize that there are non-visible portions of electromagnetic spectrum that we can feel as heat from the sun and use for radio communications or microwave ovens. In microwave and radio frequency (RF) technology antennas play a key role in efficiently transmitting and receiving electromagnetic signals. Modern-day life would be unthinkable without them as they are used in a large diversity of systems, including radio and television broadcasting, the Internet, mobile-phone communication, the wireless card in your computer and space exploration. The operation of antennas relies on the ability of an electromagnetic wave to resonantly oscillate currents in a metallic wire (or vice versa). This fact was understood and demonstrated by early radio pioneers Tesla and Marconi. Currently, the same basic antenna operation can be used to concentrate and trap light in solar cells or enable more light to escape from light sources. Since the wavelength (color) of light is much smaller than radio waves, correspondingly smaller antennas are needed to boost the efficiency of such solar cells and sources.

Our technology shows enormous potential to change the current design and operation of many devices via a simple TCO+ coating. This coating uses both the excellent electrical as well as the powerful optical properties of metals for the first time to enable simultaneous electrical current extraction and light concentration.