Flipping Photons Backward: Reversed Cherenkov Radiation Inspired by Metamaterials

Charged particles traveling through a conventional medium at a speed greater than the speed of light in the medium produce Cherenkov radiation in the forward directions, which is useful for particle identification and counting. Newly designed metamaterial, with their negative index of refraction, flips the radiated photons backward and thus readily separates the radiation from the emitting particles, providing high flexibility in the manipulation of the photons. Here we review the recent advances in reversed Cherenkov radiation research and discuss the potential that metamaterial may hold for developing new types of devices.