Flipping a photonic shock wave

Abstract

When charged particles such as electrons travel through a dielectricmedium with a speed greater than the phase velocity of the lightin the medium, electromagnetic radiation is emitted that falls intoa cone fanning out in the forward direction [Fig. 1, top left]. Thisphenomenon is called cerenkov radiation, named after the Russianscientist who first characterized it rigorously and was awarded theNobel Prize in Physics in 1958. Most people are familiar with cerenkovradiation from the blue glow of an underwater nuclear reactor asit emits energetic charged particles. The angle of the cerenkov emissioncone is related in a simple way to the particle velocity. This uniquefeature enables a wide range of applications, from the measurementof fast particles in high-energy physics, the characterization offission rate in nuclear reactors, to the detection of labeled biomolecules.Now in a paper appearing in Physical Review Letters, Sheng Xi andcolleagues at Zhejiang University, China, and the Massachusetts Instituteof Technology, US, experimentally demonstrate that the directionof the cone of cerenkov radiation can be reversed in artificiallyengineered composite media, namely, metamaterials [1].