Nat. Phys. http://doi.org/crv7 (2018)

Cherenkov radiation — light emission that occurs when a charged particle propagates through a medium at a speed that is faster than the phase velocity of light in the medium — is of importance to applications such as particle detection. However, the relation between the angle of Cherenkov emission and the particle velocity is inherently limited by the refractive index of the material. Now, an international team led by Xiao Lin has removed this restriction by using a one-dimensional photonic crystal to control the Cherenkov angle at will. The photonic crystal was constructed by alternating two transparent dielectric materials, and the Cherenkov angle can be engineered to be suitable for particle identification of high momenta near 500 GeV/c , which is hard to achieve with a conventional Cherenkov detector. Another advantage of the one-dimensional photonic crystal approach is that the crystal only needs to be a few millimetres thick.