Transition bremsstrahlung of relativistic particles

High frequency (ω > > ωsub(pe) = (4πnesup(2)/msub(e))sup(1/2)) bremsstrahlung of electromagnetic waves in a plasma or condensed media are investigated in the quasi-classical limit. Scattering of virtual photons by the proper charge of the test particle (common or Compton bremsstrahlung) as well as by dynamic polarization (transition bremsstrahlung) is taken into account. The freqeuncy ranges are studied in which interference occurs between radiation corresponding to the usual Compton bremsstrahlung and radiation corresponding to transition bremsstrahlung. The limits of applicability of the Bethe-Heitler formula for a plasma are determined and it is shown that in the low frequency range bremsstrahlung in a plasma is completely determined by a novel transition mechanism and the above formula is not valid