title: Laser light triggers increased Raman amplification in the regime of nonlinear Landau damping.
abstract: Stimulated Raman backscattering (SRS) has many unwanted effects in megajoule-scale inertially confined fusion (ICF) plasmas. Moreover, attempts to harness SRS to amplify short laser pulses through backward Raman amplification have achieved limited success. In high-temperature fusion plasmas, SRS usually occurs in a kinetic regime where the nonlinear response of the Langmuir wave to the laser drive and its host of complicating factors make it difficult to predict the degree of amplification that can be achieved under given experimental conditions. Here we present experimental evidence of reduced Landau damping with increasing Langmuir wave amplitude and determine its effects on Raman amplification. The threshold for trapping effects to influence the amplification is shown to be very low. Above threshold, the complex SRS dynamics results in increased amplification factors, which partly explains previous ICF experiments. These insights could aid the development of more efficient backward Raman amplification schemes in this regime.
authors.affiliation: CEA, DAM, DIF, F- 91297 Arpajon, France.
authors.forename: S
authors.initials: S
authors.lastname: Depierreux
authors.affiliation: 1] CEA, DAM, DIF, F- 91297 Arpajon, France [2] LULI, UMR 7605 CNRS-Ecole Polytechnique-CEA-Université Paris VI, 91128 Palaiseau Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Yahia
authors.affiliation: CEA, DAM, DIF, F- 91297 Arpajon, France.
authors.forename: C
authors.initials: C
authors.lastname: Goyon
authors.affiliation: LULI, UMR 7605 CNRS-Ecole Polytechnique-CEA-Université Paris VI, 91128 Palaiseau Cedex, France.
authors.forename: G
authors.initials: G
authors.lastname: Loisel
authors.affiliation: CEA, DAM, DIF, F- 91297 Arpajon, France.
authors.forename: P-E
authors.initials: PE
authors.lastname: Masson-Laborde
authors.affiliation: P. N. Lebedev Physical Institute, 53 Leninskii Prospect, Moscow 119991, Russia.
authors.forename: N
authors.initials: N
authors.lastname: Borisenko
authors.affiliation: P. N. Lebedev Physical Institute, 53 Leninskii Prospect, Moscow 119991, Russia.
authors.forename: A
authors.initials: A
authors.lastname: Orekhov
authors.affiliation: Helmotzzentrum fur Schwerionenforschung GSI, 64291 Darmstadt, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Rosmej
authors.affiliation: Helmotzzentrum fur Schwerionenforschung GSI, 64291 Darmstadt, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Rienecker
authors.affiliation: LULI, UMR 7605 CNRS-Ecole Polytechnique-CEA-Université Paris VI, 91128 Palaiseau Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Labaune