Reaching nonlinear regime in Raman amplification of ultrashort laser pulses

In this paper, we present, for the first time, clear evidence of reaching the nonlinear regime of Raman Backscattering (RBS) amplification with pulse intensity amplification exciting 1000 in 2 mm long plasma and exciting pump intensity by more than order of magnitude. We have demonstrated energy amplification of up to ∼5000 for a seed with a low input energy (<0.2 pJ) and up to ∼60 for a seed with high input energy (7.5 pJ). The output energy grew exponentially when the input was low and the gain indicated "saturation" when the input was high.