ELECTRON PARAMETRIC-INSTABILITIES OF ULTRAINTENSE LASER-PULSES PROPAGATING IN PLASMAS OF ARBITRARY DENSITY

The dispersion relation for electron parametric instabilities of a cir cularly polarized laser wave of arbitrary intensity is established wit hout restrictions on the plasma density. It is obtained in an implicit analytical form and solved numerically. The well-known stimulated Ram an scattering, relativistic modulational instability, relativistic fil amentation instability, and two-plasmon decay are recovered at low int ensity. Their behavior in the ultrarelativistic regime is characterize d by a wide extent of the unstable region in the wave vector space, wi th growth rates equal to a fraction of the laser frequency, and a stro ng harmonic generation. Particle-in-cell simulations confirm these res ults and show that the instability leads to a very strong heating of t he plasma. (C) 1997 American Institute of Physics.