Backward Raman amplification in a partially ionized gas (original) (raw)
Related papers
Raman laser amplification in preformed and ionizing plasmas
Laser and Particle Beams, 2005
The recently proposed backward Raman laser amplification scheme utilizes the stimulated Raman backscattering in plasma of a long pumping laser pulse to amplify a short, frequency downshifted seed pulse. The output intensity for this scheme is limited by the development of forward Raman scattering (FRS) or modulational instabilities of the highly amplified seed. Theoretically, focused output intensities as high as 10 25 W/cm 2 and pulse lengths of less than 100 fs could be accessible by this technique for 1 µm lasers ⎯ an improvement of 10 4-10 5 in focused intensity over current techniques. Simulations with the particle-in-cell (PIC) code Zohar are presented which investigate the effects of FRS and modulational instabilities and of Langmuir wave breaking on the output intensity for Raman amplification. Using the intense seed pulse to photoionize the plasma simultaneous with its amplification (and hence avoid plasmas-based instabilities of the pump) is also investigated by PIC simulations. It is shown that both approaches can access focused intensities in the 10 25 W/cm 2 range.
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.
Operating regime for a backward Raman laser amplifier in preformed plasma
Physics of Plasmas, 2003
A critical issue in the generation of ultraintense, ultrashort laser pulses by backward Raman scattering in plasma is the stability of the pumping pulse to premature backscatter from thermal fluctuations in the preformed plasma. Malkin et al. ͓Phys. Rev. Lett. 84, 1208 ͑2000͔͒ demonstrated that density gradients may be used to detune the Raman resonance in such a way that backscatter of the pump from thermal noise can be stabilized while useful Raman amplification persists. Here plasma conditions for which the pump is stable to thermal Raman backscatter in a homogeneous plasma and the density gradients necessary to stabilize the pump for other plasma conditions are quantified. Other ancillary constraints on a Raman amplifier are also considered to determine a specific region in the T e-n e plane where Raman amplification is feasible. By determining an operability region, the degree of uncertainty in density or temperature tolerable for an experimental Raman amplifier is thus also identified. The fluid code F3D ͓R. L. Berger et al., Phys. Plasmas 5, 4337 ͑1998͔͒, which includes the effects of thermal fluctuations, is used to verify these analytic estimates.
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.
Intense laser pulse amplification using Raman backscatter in plasma channels
Physics Letters A, 2002
It has been proposed that the Raman backscatter interaction in a plasma can be used to amplify ultra-intense laser pulses. To accomplish this, energy is transferred from a long drive pulse at frequency ω pump to an intense seed pulse at frequency ω seed , with a Langmuir plasma wave at frequency w p mediating the transfer; the frequencies are chosen to satisfy the resonant condition ω p = ω pump − ω seed. Diffraction of the pulses limits the interaction length in a uniform plasma, and hence the energy transfer between the pulses. However in a parabolic plasma density channel it is shown, through two-dimensional particle-incell simulations, that such a plasma channel can be used to guide both the amplified and drive pulses over an interaction distance much greater than a diffraction length. The seed pulse is amplified by a factor of more than 200 in energy for pulses whose widths are matched to the channel size, and achieve a peak intensity of more than 6 × 10 17 W/cm 2. Unmatched pump pulses are seen to generate much smaller gain.
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.
Laser duration and intensity limits in plasma backward Raman amplifiers
Physics of Plasmas, 2012
The shortest duration and the largest non-focused intensity of laser pulses produced by means of backward Raman amplification (BRA) in plasmas are calculated. These limits occur in moderately undercritical plasmas and are imposed by combined effects of moderately small group velocity dispersion and relativistic electron nonlinearity of the amplified pulses. The efficient BRA range covered by this theory is broader than one known previously. This can be useful for BRA of x-ray pulses in regular or compressed solids and ultra-powerful optical pulses in the lowest density solids. V
Demonstration of detuning and wavebreaking effects on Raman amplification efficiency in plasma
Physics of Plasmas, 2008
A plasma-based resonant backward Raman amplifier/compressor for high power amplification of short laser pulses might, under ideal conditions, convert as much as 90% of the pump energy to the seed pulse. While the theoretical highest possible efficiency of this scheme has not yet been achieved, larger efficiencies than ever before obtained experimentally ͑6.4%͒ are now being reported, and these efficiencies are accompanied by strong pulse compression. Based on these recent extensive experiments, it is now possible to deduce that the experimentally realized efficiency of the amplifier is likely constrained by two factors, namely the pump chirp and the plasma wavebreaking, and that these experimental observations may likely involve favorable compensation between the chirp of the laser and the density variation of the mediating plasma. Several methods for further improvement of the amplifier efficiency in current experiments are suggested.
Key plasma parameters for resonant backward Raman amplification in plasma
The European Physical Journal Special Topics, 2014
Backward Raman amplification and compression in plasma enables pulse compression to intensities not available using material gratings. In order to achieve the highest intensities and efficiencies in the compression effect, in a manner robust both to noise and other competing plasma effects, both resonance effects and detuning effects are exploited. Here we offer a simplified guide to how some of the key plasma parameters and laser parameters should be picked in order to achieve robust and efficient amplification.