Two Plasmon Decay of Laser in a Rippled Density Plasma

We develop an analytical formalism of two‐plasmon decay (TPD) of laser in a rippled density plasma. The density ripple could be produced by using a machining laser beam or it could be the ion acoustic wave produced in the stimulated Brillouin scattering process. The density ripple couples with the decay Langmuir waves (of the TPD process), producing short wavelength space charge quasi‐modes, heavily Landau damped on electrons. The quasi‐modes act as energy drains on the Langmuir waves and enhance their damping rates (nearly as the square of amplitude of ripple density). This leads to a higher threshold laser intensity for the onset of TPD and a reduction in the growth rate of the parametric instability. The effect is more pronounced at higher electron temperatures.