The cloak that renders one invisible is a common element in mythology and fairy-tales, but new materials with surprising properties bring the idea closer to reality by providing novel ways of manipulating light.
The development of structured synthetic materials with unusual electromagnetic properties, so-called metamaterials, promises to provide access to special physical effects of great technological interest. Metamaterials have already been fabricated that have a negative refractive index for electromagnetic waves – bending them in the opposite sense to light waves entering water, for instance – which opens up completely novel opportunities for the manipulation of light. One of these makes it possible, in principle, to create cloaking devices that seem to make objects disappear. Indeed, such an invisibility cloak has already been realized for microwaves.
The first attempts to overcome the technical hurdles depended on the use of elaborate nanotechnological methods that cannot easily be scaled up. However, the researchers have now synthesized metamaterials based on organic molecules as building blocks. This approach has several advantages over the metallic nanostructures previously used, as the synthetic procedures are more efficient, the components are smaller and their structures can be varied at will. The special geometry required for their metafunction is created entirely by chemical means.
The necessary electromagnetic resonances arise from the presence in the compound of chromophores, which give the molecule a characteristic color. Chromophores resonantly absorb light in the visible portion of the spectrum. The crucial feature of the newly synthesized molecules is that they contain chromophore electron systems that are arranged in parallel, separated by spacers that permit length-dependent control of interactions between chromophores. This particular spatial configuration alters the refractive properties of the new materials, and in ways that give rise to novel effects. If the sign of the refractive index can be turned negative, light impinging on the material is bent in the opposite direction to light that interacts with a naturally occurring material or medium. “So metamaterials could guide rays of visible light around an object, effectively rendering it invisible,” says the researcher.
Although this goal is still some way off, the new organic metamaterials provide the thread from which an invisibility cloak might one day be woven. The fabric itself can perhaps be put together with the help of suitable liquid-crystal structures. At all events, further work on the design of enhanced metamaterials is underway.
This story is reprinted from material from LMU Munich, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.