EMISSION IN VACUUM OF CHERENKOV RADIATION PRODUCED ON LONGITUDINAL WAVES IN A MEDIUM

Emission of light from an electron moving into vacuum from a medium with spatial dispersions is considered. The additional boundary conditions required in order to take into account space dispersion are discussed. It is shown that along with transition radiation emitted into vacuum, under certain conditions Cherenkov radiation produced in a medium on longitudinal waves may also be emitted. The angular distribution of this radiation for a weakly absorbing medium fs defined by the refraction law together with the condition for Cherenkov radiation in the medium. The main contribution to the transition radiation is from Cherenkov radiation on longitadinal waves produced in a medium near the interface (over a distance of the order of a wave length). At large distances from the interface this part of the Cherenkov radiation is a spherfcal wave restricted to a narrow frequency range lying near the plasma frequency. (auth)