Efficient Raman amplification into the PetaWatt regime
  Raman amplification of a short laser pulse off a long laser beam has been demonstrated successfully for moderate probe intensities ($\sim 10^{16}$ W/cm$^2$) and widths ($\sim 50$ micron). However, truly competitive intensities can only be reached if the amplification process is carried out at much higher probe intensities ($10^{17}-10^{18}$ W/cm$^2$ after amplification) and widths (1-10 mm). In this paper we examine the opportunities and challenges provided by this regime through the first 2-dimensional particle-in-cell simulations using wide pulses. A parameter window is identified in which a 10 TW, 600 $\mu$m wide, 25 ps long laser pulse can be efficiently amplified to 2 PW peak intensity. 
R.M.G.M. Trines, F. Fi\'uza, R. Bingham, R.A. Fonseca, L.O. Silva,   R.A. Cairns, P.A. Norreys