Phase-matched relativistic second harmonic generationin a plasma.

Abstract

An intense laser radiation (w1, � k1) propagating through a plasma at an angle to the density ripple (01, � k0) produces current and density perturbation at (w1, � k1+ � k0). The density perturbation combines with the oscillatory velocity at (w1, � k1) to produce nonlinear current at (2w1,(2 � k1+ � k0)), driving a second harmonic electromagnetic radiation. For a specific ripple wave number k0 ~~ k0c, the phase-matching conditions for the second harmonic process are satisfied, leading to resonant enhancement in the energy conversion efficiency. The efficiency of the process is sensitive to the angle between the density ripple and the incident laser and beam energy.