Raman amplification in plasma: Wavebreaking and heating effects

A three-wave model has been developed to investigate the influence of wavebreaking and thermal effects on the Raman amplification in plasma. This has been benchmarked against a particle-in-cell code with positive results. A new regime, the 'thermal chirp' regime, has been identified and illustrated. Here the shift in plasma resonance due to heating of the plasma by a monochromatic pump allows a probe pulse to be amplified and compressed without significant pump depletion. In regimes where damping dominates, it is found that inverse bremsstrahlung dominates at high densities, and improved growth rates may be achieved by preheating the plasma. At low densities or high pump intensities, wavebreaking acts to limit amplification. The inclusion of thermal effects can dramatically reduce the peak attainable intensity because of the reduced wavebreaking limit at finite temperatures.