A light-bending material designed by researchers at Chalmers University of Technology in Sweden could facilitate the search for new particles.
The metamaterial consists of thin metal disks of a few tenths of nanometers thickness, separated by a transparent material. “In this way, we create a new material that has properties that are neither those of the metal nor of the transparent material,” says Philippe Tassin, professor of applied physics at Chalmers.
Making particles collide in an accelerator creates bursts of common and rare particles that are difficult to distinguish. To identify these particles, which are invisible to the eye, scientists must identify the cone of light formed around a particle that travels faster than light in a transparent material. This is known as Cherenkov radiation, emitted when a charged particle (e.g., an electron) moves through a material at a speed higher than the speed of light in the same material. In vacuum, nothing can travel faster than the speed of light. In materials, however, light propagates slower. Thus, particles may move faster than light without violating the laws of physics.
“When this happens, a kind of shock wave is generated, similarly to a sonic shock wave created by a plane that goes through the sound barrier,” explains Tassin. The shape of that shock wave is a cone, the Cherenkov cone. The problem is that the light cone angle has a limit, and all particles with high momentum generate light cones with the same angle, making them indistinguishable. “With our metamaterial, we can change the shape of the cone if a charged particle travels through it.” As a result, even particles with high momentum can get a distinct light cone angle.
The research is detailed in the article “Controlling Cherenkov Radiation with Transformation-Optical Metamaterials,” in Physical Review Letters.
To design the new metamaterial, Tassin and his colleagues employed transformation optics, a method to construct optical devices based on techniques borrowed from Albert Einstein’s theory of general relativity. “Basically, we first imagine that space is distorted and curved — mathematically described by a transformation of space and time; hence the name — and light does not propagate along straight lines,” Tassin says. “Then we can convert this complex space into a material with very specific properties. The most challenging part is normally the design of a material with exactly the properties as prescribed by transformation optics.”
In the future, the expert projects, Cherenkov radiation and similar phenomena may be used for the generation of lights on chips, in particular to create light sources with a subwavelength aperture. Transformation optics can be used to improve the properties of such light sources.
Tassin’s team will continue their work on extending the application possibilities of transformation optics and on designing the metamaterials that are necessary to implement transformation-optical systems.
Written by Sandra Henderson, research editor Novus Light Technologies Today