An aerial for light

Austrian physicists report unusual light-metal interaction

A team under Professor Franz Aussenegg at the University of Graz in Austria is looking into unusual interactions between light and submicroscopic metal particles. The physicists’ findings represent a major advance towards the development of improved data storage media and optical sensors. They also confirmed theoretical predictions and merited publication in 13 international scientific journals. These are the impressive results of a two-year project funded by the Austrian Science Fund (FWF) that has been investigating the nano-cosmos.

“There’s plenty of room at the bottom,” said American Nobel Prizewinner Richard P. Feynman back in 1959. By “the bottom” he meant the world of things that are too small to see, and his point is proved by today’s computer chips, which are constantly becoming smaller yet can process increasing amounts of data, and the steadily growing capacity of CDs and DVDs. However data processing in ever tinier dimensions calls for new technologies. One of these, nano-optics, which uses light, is being researched into by Prof. Aussenegg’s team at the University of Graz Institute for Experimental Physics in Austria.

“For physical reasons guiding light with the help of lenses, mirrors or prisms is no longer possible when you get down to millionths of millimetres — the nanoworld,” said the Institute’s director, Aussenegg. “But this is the level where light — or to be more precise, optoelectrical fields — can be led through solid materials. In principle, it’s like guiding radio and TV signals through aerials and cables.” This is possible because light enters into a fascinating interaction with metal at the nanometre level. It is no longer reflected but instead excites electrons near the surface of the metal, causing them to oscillate. For a short time the light is “captured“ in the metallic structure, as an electrical field. If this “surface plasmon” state lasts long enough the optoelectrical oscillations in the metal can be channelled, as though they were travelling along a nanoscopic wire. This is crucial to the prospects of nano-optics as a practical technology.

The Graz project, completed in December 2002, succeeded in demonstrating that it is possible to influence the duration of the oscillating state of electrons near the surface of a grating-like structure of metal particles that are a few millionths of a millimetre apart from each other. The FWF backed project investigated the influence of the precise dimensions of gold and silver gratings. It provided convincing confirmation of the theoretical prediction that the right ratio of the spacing of the metal particles and their size to the wavelength of the light would quadruple the duration of the oscillation.

The team’s findings have laid the groundwork for the use of light as an alternative to electrotechnology in telecommunications engineering, data processing and data storage. The results have already opened the way for improved data storage media and optical sensors. The researchers’ work has attracted widespread attention, as shown by an article published on 24 October in the online version of Britain’s Economist magazine which spoke of a “significant step towards properly integrated optoelectronics”. Again and again, the origins of industrial revolutions have lain in fundamental research, and the breakthrough in Graz could be the start of another.

Bildunterschrift: The principle of the surface plasmon: light spreads outwards on a nanoscopic metal surface similarly to a wave in water.