Multibeam Raman amplification of a finite-duration seed in a short distance

A new scheme of multibeam Raman amplification(MRA)is proposed in virtue of the collective mode by sharing a common scattered light.Multiple laser beams can provide a higher growth rate,but the overlapping region limits the amplification length.We suggest to use a finite-duration seed to facilitate MRA in a short distance.Through two-dimensional particle-in-cell simulations,we find that two-beam Raman amplification has a much higher growth rate than that of singlebeam one.This growth rate depends on the initial seed amplitude,electron temperature,and seed duration.An empirical criterion,γ0τc=1,whereγ0 is the theoretical growth rate of MRA,is used to choose a proper duration for a higher growth rate.After a total amplification length of 320µm,the two-beam Raman amplification shows nonlinear features of pulse compression and a bow-shape wave front,indicating that the amplification has finally entered the self-similar regime.