Fine structure of Vavilov-Cherenkov radiation near the Cherenkov threshold

We analyze the Vavilov-Cherenkov radiation (VCR) in a dispersive nontransparent dielectric air-like medium both below and above the Cherenkov threshold, in the framework of classical electrodynamics. It is shown that the transition to the subthreshold energies leads to the destruction of electromagnetic shock waves and to the sharp reduction of the frequency domain where VCR is emitted. The fine wake-like structure of the Vavilov-Cherenkov radiation survives and manifests the existence of the subthreshold radiation in the domain of anomalous dispersion. These domains can approximately be defined by the two phenomenological parameters of the medium, namely, the effective frequency of oscillators and the damping describing an interaction with the other degrees of freedom.Comment: 9 pages, 6 figure

Observation of the interference of two transition radiations emitted by ultra-relativistic lead ions in a gas close to the Vavilov- Cherenkov radiation threshold

The interference of two transition radiations emitted by ultra- relativistic lead ions in a gas near the Vavilov-Cherenkov radiation threshold was observed. The experiment was performed at 158 A GeV lead ion beam of CERN SPS. The experimental results are in good agreement with Tamm's theory. (6 refs)