Physicists at the Zhejiang University, in China, and the Massachusetts Institute of Technology (MIT), in the US, have recently discovered a reverse shock wave of light forming in a special type of structure, known as a left-handed metamaterial. This is the first time the effect is directly observed in such a specifically tailored batch of material. The observation was predicted theoretically more than 40 years ago, but all attempts at seeing it have failed until now.

In a new paper detailing the finds that appears in the latest issue of the journal Physical Review Letters, and that is also highlighted with a Viewpoint in the November 2 issue of Physics, the experts add that the elusive physical phenomenon that has now been proven is called the Cherenkov radiation. The shock wave that is formed in the shape of a cone of light, which represents the radiation, is produced because light does not travel through objects at the same speed it does through a void.

As it moves through air or glass, for example, some electrons or other charged particles in the medium may, for the briefest of moments, surpass the speed that the photons have. This produces the shock wave that Russian expert Pavel Alekseyevich Cherenkov characterized in detail. His research on the matter granted him the 1958 Noble Prize in Physics. The radiation can most often be seen in nuclear reactors, and looks like a “blue glow,” as those working in nuclear power plants say.

The thing about the new experiments is that they did not look at the Cherenkov radiation that formed in regular mediums, but in left-handed metamaterials. As a class, these materials have a very peculiar effect on light, as demonstrated by the fact that they are currently used to create invisibility cloaks, and the research is progressing rapidly. The left-handed version affects light in an opposite manner from regular, right-handed materials. This means that, theoretically, the light cones produced by the photons in the radiation should have traveled backwards from regular cones.

In their investigations, the experts used an optical structure to simulate particles moving at twice the speed of light, rather than injecting faster-than-light particles into the material. This allowed for the production of very powerful Cherenkov radiations, which were then picked up by special instruments. The work also showed potential new uses for left-handed metamaterials, especially in high-energy particle accelerators and in other such scientific experiments.