Vavilov-Cherenkov radiation in dispersive medium

We analyze how the frequency dependence of the electric permittivity epsilon affects the electromagnetic field radiated by a point charge uniformly moving in a medium. It turns out that a moving charge radiates at every velocity when the standard parametrization of epsilon is chosen. The space distribution of this radiation exhibits rapid oscillations behind the moving charge. They differ drastically for the charge velocity below and above some critical velocity v(c) defined by the medium properties and independent of frequency. It turns out that for v < v(c) the radiation flux is maximal in the narrow cone lying behind the moving charge with the axis coinciding with the charge velocity. The influence of the imaginary part of electric permittivity epsilon on the electromagnetic field radiated by a moving charge is also studied. It turns out that switching on the imaginary part of epsilon results in a considerable reduction of the intensity of radiation for v < v(c) and in attenuation of secondary maxima of the radiation intensity for v > v(c). This consideration may be useful for the interpretation of experiments recently discussed in physics literature. (C) 1999 Elsevier Science B.V. All rights reserved.