Observation of the reversed Cherenkov radiation.

Reversed Cherenkov radiation is the exotic electromagnetic radiation that is emitted in the opposite direction of moving charged particles in a left-handed material. Reversed Cherenkov radiation has not previously been observed, mainly due to the absence of both suitable all-metal left-handed materials for beam transport and suitable couplers for extracting the reversed Cherenkov radiation signal. In this paper, we develop an all-metal metamaterial, consisting of a square waveguide loaded with complementary electric split ring resonators. We demonstrate that this metamaterial exhibits a left-handed behaviour, and we directly observe the Cherenkov radiation emitted predominantly near the opposite direction to the movement of a single sheet electron beam bunch in the experiment. These observations confirm the reversed behaviour of Cherenkov radiation. The reversed Cherenkov radiation has many possible applications, such as novel vacuum electronic devices, particle detectors, accelerators and new types of plasmonic couplers.