Stimulated Brillouin rescattering

Speziale, Thomas; Mcgrath, Joseph F.; Berger, R. L.

doi:10.1063/1.863127

Cited by 24 publications

(10 citation statements)

References 5 publications

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“…cs ) propagating IAWs. relating to the backward traveling IAW is due to Brillouin backscatter of the reflected wave itself [12]. This mechanism manifests itself only at sufficiently high intensity.…”

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confidence: 99%

Low-Level Saturation of Brillouin Backscattering due to Cavity Formation in High-Intensity Laser-Plasma Interaction

2005

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Full particle-in-cell simulations of Brillouin backscattering in the high-intensity regime are presented. The final state of the strongly nonlinear evolution of the ion-acoustic wave packet consists of its collapse and the formation of a density cavity which is supported by large-amplitude localized electromagnetic fields. The cavitation manifests itself in large oscillations of the reflectivity which is terminated by a low-level saturation with strong kinetic effects. This newly discovered scenario demonstrates the importance of fully kinetic descriptions of Brillouin backscattering for high intensities.

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confidence: 99%

Low-Level Saturation of Brillouin Backscattering due to Cavity Formation in High-Intensity Laser-Plasma Interaction

2005

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“…This four-mode case (curve b) where the rescattered light grows from the noise level can be considered as the natural rescattering case already investigated. 13 As I said before it does not differ significantly from the single-scattering or classical two-mode case (dotted curve a in Fig. 2) commonly studied for the pump-depletion mechanism.…”

Section: = [L 2 (X)i 4 {X)/l 1 (X)]sinhc 2 {X+ C\) Exp(dx/2)mentioning

confidence: 81%

“…This multihumped intensity-decreasing spectrum does not coincide with the multiline spectrum already investigated, 8 ' 11 ' 12 since the spread between the lines must be 2Aco BS (which for a T e = T i = 200-eV plasma is given by 2Act> BS /a> 0 ^2xl0~3) and not only greater than y. Natural rescattering of the single-pump pulse has been investigated by Speziale, Mc Grath, and Berger, 13 who conclude that it is not an effective process for small noise levels because the rescattered wave must grow from a small amplitude as it propagates in the direction of decreasing backscattered intensity. This is the case for natural rescattering on the noise level, but the frame completely changes if we force rescattering or multiple scattering by additional downshifted pump spectra.…”

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confidence: 91%

Efficient Way to Prevent Reflection from Stimulated Brillouin Backscattering

Montes¹

1983

Phys. Rev. Lett.

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The same physical mechanism which causes stimulated Brillouin backscattering of a laser pulse when interacting with the underdense plasma (in laser fusion systems) can be used to reverse the scattering direction in order to drastically reduce the reflectivity. Forced stimulated rescattering may be obtained by additional radiation pulses or by a multihumped spectrum with each peak down-shifted by twice the acoustic frequency. Analytical four-mode and numerical six-mode models show strong reduction of the reflectivity for the same input intensity.PACS numbers: 52.25.Ps, 52.35.Mw, 52.40.Db, 52.50.Jm In laser-plasma interaction experiments on inertial fusion devices, a problem of importance is the stimulated backscattering of the incident radiation since this effect is capable of reflecting a large fraction of the laser energy incident on a fusion target and may reduce the coupling efficiency. Theoretical and numerical calculations suggest that intense laser radiation interacting with ion-acoustic waves in the underdense coronal plasma surrounding the target may lead to strong stimulated Brillouin (back-)scattering (SBS). 1 " 4 The physical mechanism may be interpreted as a parametric instability where the incident laser wave of frequency oo 0 and wave vector k 0 resonantly drives a backscattered electromagnetic wave at oo R = 0 /c, whereThe instability occurs because the ponderomotive force generated by the superposition of the ingoing and backscattered waves satisfies the matching conditions for frequency (energy) and wave vector (momentum). 4 In the heavy sound wave damping limit (y ia >^ia; ZT e ~T;), for which I shall present my results, the acoustic intensity remains approximately proportional to the product of the ingoing-and backscattered-wave intensities.Since these intensities decay in the forward direction because of pump depletion, the acoustic intensity builds up from its boundary value to a peak value of the order of the attenuation length l s = y ia /c s and then decays in the forward direction for the remaining part of the interaction region. The instability is convective, 1,3 SBS merges to stimulated-ion-Compton scattering 3 (SICS), and the backscattered radiation which was downshifted by the acoustic frequency o; ia becomes now downshifted by the ion-Doppler width Aco D . = 2(KT { /m i c 2 ) l/2 u) 0 . I shall call Aco BS the effective backscattered downshift which can be modified by plasma motion and light reflection from the critical surface. 5 Experiments with Ndrglass lasers show that SBS can reflect large amounts of laser light. 6 It may attain up to 60% in longpulse C0 2 lasers 7 interacting with an underdense millimeter-length hydrogen plasma at intensities of 10 13 W/cm 2 . Widely varying conditions are involved for the saturation mechanism, 4 but reflectivity from SBS remains important when the threshold for the backscatter instability is well overcome....

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“…In neither case do we treat the secondary scattering problem but we refer those interested to previous treatments. 5 The procedure for obtaining Eqs. (1) in either limit is straightforward and will not be given here.…”

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confidence: 99%

“…These invariants also were found in the study of rescattering. 5 The case where I f =0 or p -°o has been studied by Tang 6 who shows that the reflectivity increases monotonically with plasma length L to a limiting value of 1. These equations together with Eqs.…”

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confidence: 99%

Nonlinear Competition between Stimulated Brillouin-Scattered Light Waves in Plasmas

Berger

1983

Phys. Rev. Lett.

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Nonlinear equations are solved which describe the competition between two decay modes for laser light energy. When they are applied to the competition between Brillouin forwardand backward-scattered light, multivalued solutions occur for plasmas between two limiting sizes. Application to particular experiments may explain appearance of either red-or blue-shifted peaks or both in time-integrated spectra.

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Stimulated Brillouin rescattering

Abstract: Rescattering of stimulated Brillouin scattered light is investigated. The net reflection coefficient for light scattered by a plasma slab is calculated and compared with the single scatter result.

Cited by 24 publications

References 5 publications

Low-Level Saturation of Brillouin Backscattering due to Cavity Formation in High-Intensity Laser-Plasma Interaction

Low-Level Saturation of Brillouin Backscattering due to Cavity Formation in High-Intensity Laser-Plasma Interaction

Efficient Way to Prevent Reflection from Stimulated Brillouin Backscattering

Nonlinear Competition between Stimulated Brillouin-Scattered Light Waves in Plasmas

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