jupitersterrain four

In a more complex periodic medium, such as a photonic crystal, one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction whereas ordinary Cherenkov radiation forms an acute angle with the particle velocity

Cherenkov radiation is electromagnetic radiation emitted when a charged particle such as an electron passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The charged particles polarize the molecules of that medium, which then turn back rapidly to their ground state, emitting radiation in the process. The characteristic blue glow of nuclear reactors is due to Cherenkov radiation.  prediction considered particles hypothetically moving faster than light in vacuum

A common analogy is the sonic boom of a supersonic aircraft or bullet. The sound waves generated by the supersonic body propagate at the speed of sound itself; as such, the waves travel slower than the speeding object and cannot propagate forward from the body, instead forming a shock front. In a similar way, a charged particle can generate a photonic shock wave as it travels through an insulator


Wiki 19.13, 7.11.12.