Imitating the Cherenkov radiation in backward directions using one-dimensional photonic wires.

A novel radiation emission from traveling charged particles in vacuum is theoretically demonstrated. This radiation is conical as in the Cherenkov radiation, but emerges in backward directions of the particle trajectories. The basic mechanism of the radiation is the Smith-Purcell effect via the interaction between the charged particles and a circular-symmetric photonic wire with a one-dimensionally periodic dielectric function. The wire exhibits the photonic band structure characterized with angular momentum. The charged particle can resonantly excite the photonic band modes with particular angular momentum, depending on the particle velocity. A simple kinetics of the Smith-Purcell effect enables us to design the conical radiation emitted in backward directions. Numerical results of the backward radiation are also presented for a metallic wire with aligned air holes.