Amplification of short laser pulses by Stimulated Brillouin Backscattering T. Gangolf 1,2 , L. Lancia 3 , J.-R. Marquès 1 , A. Giribono 3 , K. Glize 1,4 , M. Blecher 2 , L. Vassura 1,3 , A. Frank 5 , M. Quinn 6 , M. Cerchez 2 , C. Riconda 7 , S. Weber 6,8 , M. Chiaramello 7 , G. Mourou 7 , O. Willi 2 , J. Fuchs 1 1 LULI, École polytechnique – CNRS – CEA – UPMC, 91128 Palaiseau, France 2 ILPP, Heinrich-Heine Universität Düsseldorf, 40225 Dusseldorf, Germany 3 Dept. SBAI, Università di Roma "La Sapienza", 00161 Rome, Italy 4 CEA, Bruyères-le-Châtel, 91297 Arpajon, France 5 GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany 6 IZEST, École polytechnique – CEA, 91128 Palaiseau, France 7 LULI, Sorbonne Universités-UPMC–École polytechnique–CNRS–CEA, 75005 Paris, France 8 Institute of Physics of the ASCR, ELI-Beamlines, 18221 Prague, Czech Republic Introduction In search for novel techniques for amplifying laser light to ever higher intensities, plasma amplification is being investigated by several groups, including the IZEST C 3 project [1]. A plasma-based approach benefits from the fact that a plasma can sustain much higher intensities than a solid state amplifier. In a plasma, energy can be transferred from one laser pulse (pump) to another (seed), either via a high-frequency plasma electron wave (stimulated Raman backscat- tering, SRS [2]) or by a low-frequency ion acoustic wave (stimulated Brillouin backscattering, SBS [3]). Especially, the strong coupling regime of SBS (sc-SBS) is of interest since seed pulses much shorter than the ion acoustic timescale λ c s ≈ 10 ps can be amplified. The strong coupling regime is reached when the the pump pulse (ω 0 , k 0 ) is so intense that the plasma response is determined by the pump pulse. For this to happen, the pump must fulfill the threshold condition (v o /v e ) 2 = 4k 0 c s ω 0 /ω 2 pe . Here, v o = eE /(ω 0 m e ) is the electron quiver ve- locity in the laser electric field E , ve =  kT e /m e the electron thermal velocity, c s =  ZkT e /m i the ion sound velocity, and ω pe =  4π n e e 2 /m e is the electron plasma frequency. In more prac- tical units, I 14 λ 2 μ m = 0.11 T 3/2 keV  Z A n c n e  1 - n e n c , (1) where I 14 is the intensity in 10 14 W cm 2 , λ μ m is the pump wavelength in μ m, T keV is the electron temperature in keV, Z is the charge number, A = m i /m e is the mass number, and n e is given in units of the critical density n c = ω 2 ε 0 m e /e 2 . Therefore, this regime is attained at high pump intensities, high plasma electron densities, and low plasma electron temperatures. 42 nd EPS Conference on Plasma Physics P2.203