Role of Frequency Chirp and Energy Flow Directionality in the Strong Coupling Regime of Brillouin-Based Plasma Amplification

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A detailed analysis of the various stages of strong coupling Brillouin plasma amplification, emphasizing the importance of the chirp which can be of threefold origin: the intrinsic one driven by the amplification process, the one originating from the chirped-pulse generated laser pulses, and the one associated with the plasma profile. It has importance to understand and control cross-beam energy transfer in inertial confinement fusion.

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Description
(a) Evolution in time of the phases of the pump (φp, blue line) and of the seed (−φs, green line) and the density perturbation (−φ, red line) in units of π. (b) Time evolution of the total phase θ = φp - φs + Φ – φ, in units of π. The green shadowed regions indicate the values of θ for which the pump amplifies the seed; the blue ones correspond to a reversed flow energy direction. (c) Electric field amplitudes, in V/m, of the pump (blue line) and of the seed (green line) as a function of time. The data are taken at xcross = 350 μm, the point where seed and pump initially collide in the plasma.