THE PHYSICS OF THE NONLINEAR OPTICS OF PLASMAS AT RELATIVISTIC INTENSITIES FOR SHORT-PULSE LASERS

The nonlinear optics of plasmas at relativistic intensities are analyz ed using only the physically intuitive processes of longitudinal bunch ing of laser energy, transverse focusing of laser energy, and photon a cceleration, together with the assumption of conservation of photons, i.e., the classical action. All that is required are the well-known fo rmula for the phase and group velocity of light in plasma, and the eff ects of the ponderomotive force on the dielectric function. This forma lism is useful when the dielectric function of the plasma is almost co nstant in the frame of the light wave. This is the case for Raman forw ard scattering (RFS), envelope self-modulation (SM), relativistic self -focusing (SF), and relativistic self-phase modulation (SPM). In the p ast, the growth rates for, RFS and SPM have been derived in terms of w ave-wave interactions. Here we rederive all of the aforementioned proc esses in terms of longitudinal bunching, transverse focusing, and phot on acceleration. As a result, the physical mechanisms behind each are made clear and the relationship between RFS and envelope SM is made ex plicitly clear. This allows a single differential equation to be obtai ned which couples RFS and SM, so that the relative importance between each process can now be predicted for given experimental conditions.