Ion acoustic nonlinearities in stimulated Brillouin scattering

Reduction of stimulated Brillouin scattering by the generation of higher ion wave harmonics is investigated. A theory model is derived which includes all harmonics. A simplified model based on the truncation to second harmonic ion waves reveals several interesting features. When damping and detuning are neglected the reflectivity is drastically reduced in a low‐density plasma (ne<0.25ncr), but the solution turns phase unstable at low reflectivity levels. Finite damping of ion waves extends the range of validity of the model. Still nonlinear damping of the primary decay may considerably exceed the linear damping, rendering the generation of the second harmonic an important mechanism. A large detuning of the second harmonic is required before it can be considered decoupled. The strong interaction between the ion waves introduces a power shift which is able to dynamically reduce the Brillouin reflectivity. Undersone parameter conditions the reflectivity approaches an oscillatory steady state. The accuracy of...

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