Two-Plasmon Decay of Self-Trapped Laser Radiation in a Plasma

A Gaussian laser beam propagating through a plasma exerts a transverse ponderomotive force on the electrons and creates a density depletion near the axis of the beam. This self-generated plasma channel supports localized Langmuir eigenmodes. The laser pump can parametrically excite two localized Langmuir waves, at reasonably low powers as the convective losses for the decay are minimal. A perturbation approach is employed to investigate the growth rate and the threshold for the decay process. The growth rate increases with the azimuthal mode number, tending to a maximum around m ~ kz (ωρ0/υthLn)1/2. However, it decreases with the radial mode number.