Professor Christopher Davis, research scientist Igor Smolyaninov, and graduate student Yu-Ju Hung at Maryland's A. James Clark School of Engineering have used plasmon technology to create the world's first invisibility cloak for visible light.
They have used the same technology to develop a revolutionary superlens microscope that enables scientists to see details of previously undetectable nanoscale objects.
The invisibility cloak refracts the light that strikes the object, so that the light moves around and past the cloak, reflecting nothing, leaving the cloak and its contents ‘invisible.’
The cloak consists of a two-dimensional pattern of concentric rings created in a thin, transparent acrylic plastic layer on a gold film. The plastic and gold each have different refractive properties.
The structured plastic on gold in different areas of the cloak creates ‘negative refraction’ effects, which bend plasmons, electron waves generated when light strikes a metallic surface under precise circumstances, around the cloaked region.
This manipulation leads the plasmon waves to appear to have moved in a straight line. In reality they have been guided around the cloak much as water in a stream flows around a rock, and released on the other side, concealing the cloak and the object inside from visible light. The invisibility is not absolutely perfect because of energy loss in the gold film.
Researchers achieved this invisibility under very specialized conditions. The cloak is just 10 micrometers in diameter; by comparison, a human hair is between 50 to 100 micrometers wide. Also, the cloak uses a limited range of the visible spectrum, in two dimensions.
Extending the cloak to three dimensions would be a significant challenge because researchers would need to control light waves both magnetically and electronically to steer them around the hidden object. The technology initially might work only for small objects of specific controlled shape.
Researchers have also used plasmonics to develop superlens microscopy technology, which can be integrated into a conventional optical microscope to view nanoscale details of objects that were previously undetectable.
The superlens microscope could one-day image living cells, viruses, proteins, DNA molecules, and other samples, operating much like a point-and-shoot camera. The new technology could revolutionize the capability to view nanoscale objects at a crucial stage of their development. The team believes they can improve the resolution of their microscope images down to about 10 nanometers, one ten thousandth of the width of a human hair.
A large reason for the success of the group's innovations in both invisibility and microscopy is that surface plasmons have very short wave lengths, and can therefore move data around using much smaller-scale guiding structures than in existing devices.
These small, rapid waves are generated at optical frequencies, and can transport large amounts of data. The group also has made use of the unique properties of metamaterials, artificially structured composites that help control electromagnetic waves in unusual ways using plasmonic phenomena.
The various applications the group has derived from their plasmonics research is an example of the ingenuity of researchers approaching new and dynamic technologies that offer broad and unprecedented capabilities.
http://www.sciencedaily.com/releases/2007/12/071218192009.htm
http://www.abc.net.au/science/articles/2003/06/12/872457.htm
http://www.cnrs.fr/insis/recherche/actualites/invisibilite.htm
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