Plasma-based amplification by strongly coupled Brillouin scattering has recently been suggested for the compression of a short seed laser to ultrahigh intensities in sub-quarter-critical-density plasmas. However, by employing detailed spectral analysis of particle-in-cell simulations in the same parameter regime, we demonstrate that, in fact, Raman backscattering amplification is responsible for the growth and compression of the high-intensity, leading spike, where most of the energy compression occurs, while the ion mode only affects the low-intensity tail of the amplified pulse. The critical role of the initial seed shape is identified. A number of subtleties in the numerical simulations are also pointed out.
Bibliographical noteFunding Information:
This work was supported by the U.S. DTRA Grant No. HDTRA1-11-1-0037, AFOSR Grant No. FA9550-15-1-0391, NNSA Grant No. DE-NA0002948, and the U.S. DOE Grant No. DE-AC02-09CH1-1466. The authors gratefully acknowledge A. A. Balakin and C. Z. Xiao for the constructive discussions. M.R.E. acknowledges the support of the NSF through a Graduate Research Fellowship. This work was partially performed at PPPL's Research Computing Center and the High Performance Computing Center at Princeton University. The development of the EPOCH code was funded in part by UK EPSRC Grant Nos. EP/G054950/1, EP/G056803/1, EP/G055165/1, and EP/M022463/1.
© 2016 Author(s).