Photon Kinetic Theory and Simulations of Laser-Plasma Interactions

The propagation of electromagnetic waves in underdense plasmas can be described by a Vlasov-like transport equation for the Wigner distribution function of the e.m.field. We determine the temporal growth rates for Raman Scattering for all angles from the photon kinetic theory, and compare them with the standard growth rates, thus establishing the limits of validity of the theory. The kinetic structure of the e.m.field propagation equation leads naturally to a ``photon in cell" numerical model. We compare 1D simulations (neglecting plasma response) and 2D simulations (using QWAKE, the photon kinetic version of WAKE (P.Mora and T.M.Antonsen, PoP 4), 217 (1997)) of ultraintense laser pulse (a₀ ~= 1) propagation in underdense plasmas, with analytic results for the pulse spread/compression, pulse steepening and the velocity of energy transport, and we find good agreement between the simulations and the theory. Applications of the photon kinetic theory to intense broadband radiation-plasma interaction will also be discussed.