Radiation by collective interaction

The bremsstrahlung of an electron passing through a plasma under the cumulative influences of long range coulomb forces exerted by many other electrons in the medium is considered. In this process, the medium exchanges a definite amount of momentum and energy with the radiating electron in the form of a plasmon. The differential cross section is obtained for the process in which a photon is emitted in a given direction and energy while the radiating electron is deflected through a given angle after exciting or absorbing a plasmon. The processes may also be looked upon as the plasmon emission or absorption processes by anomalous Doppler effect if one imagines a moving 'atom' consisting of an electron and a plasmon. The radiation condition, which is the extension of the usual Cerenkov condition in the plasma, is found to be | c/nυ ± ω_p/kυ ∓ (k_p/k) Cosθ_p |≤1, where υ is the velocity of the electron, n the refractive index, k the wave number of the emitted photon, (ω_p, k_p) the plasmon frequency and the wave number, and θ_p = υ vector k vector _p, the upper signs referring to the plasmon emission and the lower to the plasmon absorption. (author)