Theory and simulation of electronic relativistic parametric instabilities for ultraintense laser pulses propagating in hot plasmas

The dispersion relation for electronic parametric instabilities of a circul arly polarized laser wave is solved in the case where the distribution func tion is supposed to be cold in the transverse direction and to be a linear combination of a cold distribution function and of a Maxwellian in momentum in the longitudinal direction. Only densities below the critical density a re considered. It is shown that the longitudinal temperature as expected re duces the growth rate, but that the existence of a hot tail is not sufficie nt to significantly reduce the instability. It is the bulk of the distribut ion function that must be heated to efficiently stabilize the system. Anoth er important effect of the heating is to reduce the backscattered component of the instability. An example of a one-dimensional particle simulation pe rformed in the exact conditions of validity of the theory is discussed. (C) 2001 American Institute of Physics.