Wave kinetics and photon acceleration

Abstract

We review recent theoretical work on photon kinetics and wave kinetics in a plasma, where resonant interactions of waves with photons, and with quasi-particles such as plasmons, is considered. A Wigner function, or quasi-distribution function, for photons and quasi-particles, is introduced. The resulting wave kinetic equation is able to describe the evolution of a broad photon spectrum, or more generally, a turbulent plasma state, if conveniently coupled with the wave equations via ponderomotive force terms. Resonant interactions occur when the phase velocity of the large scale wave (for instance a wakefield) is equal to the group velocity of the short wavelength quasi-particles (for instance a short laser pulse). It is shown that quasi-particle Landau damping can take place, as well as quasi-particle beam instabilities. A direct link between short and large wavelength perturbations in the plasma is established. Photon and quasi-particle acceleration and trapping is also discussed.