Numerical modeling of quasitransient backward Raman amplification of laser pulses in moderately undercritical plasmas with multicharged ions (original) (raw)
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Physics of Plasmas, 2010
The range of plasma parameters, where the efficient quasitransient backward Raman amplification ͑QBRA͒ of powerful laser pulses is possible, is determined for dense plasmas with multicharged ions. Approximate scalings that portray in a simple way the efficient QBRA range in multidimensional parameter space are found. The calculation, applicable to infrared, ultraviolet, soft x-ray, and x-ray laser pulses, takes into account plasma heating by the lasers. It is shown that efficient QBRA can survive even the nonsaturated linear Landau damping of the Langmuir wave mediating the energy transfer from the pump to the seed laser pulse; moreover, this survival does not require very intense seed laser pulses.
Detuned Raman Amplification of Short Laser Pulses in Plasma
Physical Review Letters, 2000
The recently proposed scheme of so-called "fast compression" of laser pulses in plasma can increase peak laser intensities by 10 5 [ Phys. Rev. Lett. 82, 4448 (1999)]. The compression mechanism is the transient stimulated Raman backscattering, which outruns the fastest filamentation instabilities of the pumped pulse even at highly overcritical powers. This Letter proposes a novel nonlinear filtering effect that suppresses premature backscattering of the pump in a noisy plasma layer, while the desired amplification of a sufficiently intense seed persists with a high efficiency. The effect is of basic interest and also makes it robust to noise the simplest technologically fast compression scheme.
Physics of Plasmas, 2018
Taking into account the nonlinear dispersion of the plasma wave, the fluid equations for the threewave (Raman) interaction in plasma are derived. It is found that, in some parameter regimes, the nonlinear detuning resulting from the plasma wave dispersion during Raman compression limits the plasma wave amplitude to noticeably below the generally recognized wavebreaking threshold. Particle-in-cell simulations confirm the theoretical estimates. For weakly nonlinear dispersion, the detuning effect can be counteracted by pump chirping or, equivalently, by upshifting slightly the pump frequency, so that the frequency-upshifted pump interacts with the seed at the point where the plasma wave enters the nonlinear stage.
Backward stimulated Raman scattering of a modulated laser pulse in plasmas
1997
The specific features of backward stimulated Raman scattering (BSRS) of a short modulated (multi-frequency) laser pulse in underdense plasmas are studied. The effect of resonant suppression of the BSRS of higher frequency pulse components is explored. For an arbitrary pair of pulse components, in the conditions of weak coupling, it is demonstrated that the backscattering of a higher frequency laser pulse component is a five-wave resonant process at a frequency difference between the components close to the double plasma frequency. In the conditions of strong coupling the backscattering of neither pulse component is suppressed and the spectrum of the instability is not connected immediately with the details of a spectrum of a laser pulse. Numerical modelling of the BSRS of a multi-frequency laser pulse is in complete agreement with the analytical predictions.
Physics of Plasmas, 2002
The propagation of a short and intense laser pulse ͑1.057 m, 350 fs, 10 17 W/cm 2-2 ϫ10 19 W/cm 2) through preformed undercritical plasmas ͑Ϸ5%-40% of n c) has been experimentally investigated on the 100-TW laser facility at the Laboratoire pour l'Utilisation des Lasers Intenses. The transmission and reflection of the 1 m laser pulse, the forward-and backward-Raman ͑respectively, F-SRS and B-SRS͒ scattered light and the emission of fast electrons are reported. Significant absorption occurs in these plasmas, which is found to increase with the laser intensity. B-SRS is strongly driven at 10 17 W/cm 2 and gradually decreases at higher intensities. It is shown that the transmission is low and only weakly dependent on the laser intensity. In contrast, the forward Raman scattering continuously increases with the laser intensity, up to 7% of the incident energy at 2ϫ10 19 W/cm 2 in the lowest density case. The relativistic electrons accelerated in the forward direction appear to be correlated with the F-SRS. The experimental data are discussed in the light of recent theoretical and numerical investigations, indicating that intense electron heating is likely to play a major role in the temporal growth or inhibition of the instabilities. The theoretical predictions are in agreement with the experiments.
Laser Pulse Compression in Plasma Using Coherent Raman Cascade
OSA Technical Digest (CD) (Optical Society of America, 2005), paper JThD4., 2005
Compressing laser beams in plasmas via coherent Raman sideband generation is proposed. Electron density perturbations driven by the laser beatwave broaden the laser spectrum. Chirped beatnotes are compressed in plasma with high group velocity dispersion.
Simulations of Raman laser amplification in ionizing plasmas
Physics of Plasmas, 2003
By using the amplifying laser pulse in a plasma-based backward Raman laser amplifier to generate the plasma by photoionization of a gas simultaneous with the amplification process, possible instabilities of the pumping laser pulse can be avoided. Particle-in-cell simulations are used to study this amplification mechanism, and earlier results using more elementary models of the Raman interaction are verified [D.S.Clark and N.J.Fisch., Phys.Plasmas, 9(6):2772-2780, 2002]. The effects (unique to amplification in ionizing plasmas and not included in previous simulations) of blue-shifting of the pump and seed laser pulses and the generation of a wake are observed not significantly to impact the amplification process. As expected theoretically, the peak output intensity is found to be limited to I ∼ 10 17 W/cm 2 by forward Raman scattering of the amplifying seed. The integrity of the ionization front of the seed pulse against the development of a possible transverse modulation instability is also demonstrated.
2005
The compression of a laser pulse by amplification of an ultra short pulse beam which seeds the stimulated Raman scatter of the first beam has been long been discussed in the context of solid and gas media. We investigate the possibility of using intersecting beams in a plasma to compress nanosecond pulses to picosecond duration by scattering from driven electron waves. Recent theoretical studies have shown the possibility of efficient compression with large amplitude, non-linear Langmuir waves driven either by SRS [1] or non-resonantly [2]. We describe experiments in which a plasma suitable for pulse compression is created, and amplification of an ultra short pulse beam is demonstrated.