The best known manifestation of Cerenkov radiation is probably the eerie blue light that is emitted when spent nuclear-fuel rods are plunged into water. The phenomenon occurs when a charged particle travels faster through a medium than light does, and the Cerenkov effect has been studied extensively over the last century.
Now Troy Stevens and co-workers at the University of Michigan in the US and the Max Planck Institute of Solid State Physics in Stuttgart, Germany, have shown that Cerenkov radiation can also be emitted by electric dipoles moving slower than the speed of light (T Stevens et al. 2001 Science 291 627).
In their recent work, Stevens and co-workers studied the radiation emitted by a spatially extended collection of electric dipoles, rather than a point particle. They created the trail of dipoles by injecting a laser pulse into a zirconium-selenide crystal 5 mm long.
But nature rarely gives a clear-cut answer and several theoretical issues remain. In the April issue of Physics World, Georgy N Afanasiev of the Joint Institute for Nuclear Research (JINR), Dubna, Russia, explains why he believes Cerenkov radiation is so fundamental and worthy of urgent research.
