Abstract
Brillouin amplification of laser pulses in plasma has been shown to be a promising approach to produce picosecond pulses of petawatt power. A key challenge is preservation of the quality of the amplified pulse, which requires control of parasitic instabilities that accompany the amplification process. At high plasma densities (/4), ponderomotive filamentation has been identified as the biggest threat to the integrity of the amplifying pulse. It has therefore been proposed to perform Brillouin scattering at densities below to reduce the influence of filamentation. However, parasitic Raman scattering can become a problem at such densities, contrary to densities above where it is forbidden. In this paper, we investigate the influence of parasitic Raman scattering on Brillouin amplification at densities below . We expose the specific problems posed by both Raman backward and forward scattering, and how both types of scattering can be mitigated, leading to an increased performance of the Brillouin amplification process.
Highlights
Plasma-based laser amplification offers a promising route to producing next-generation laser powers and intensities [1,2,3,4,5,6,7]
The amplification process exploits the parametric instabilities of Raman and Brillouin scattering in plasma
We find that the growth rate for the ponderomotive filamentation does not change with density, while the RBS growth rate increases and the Raman forward scattering (RFS) growth rate decreases with decreasing plasma density
Summary
Plasma-based laser amplification offers a promising route to producing next-generation laser powers and intensities [1,2,3,4,5,6,7]. In order to turn these processes into practical schemes for the production of high-power laser pulses, controlling the quality of the amplified pulse (smooth envelope, low-intensity prepulse) is as important as maximising its power and energy This involves reduction and control of competing instabilities, such as pump Raman backscattering, seed Raman forward scattering (RFS), filamentation and modulational instabilities. It was proposed to conduct Brillouin amplification experiments at n0/ncr = 0.3 [7], where n0 denotes the background plasma electron density and ncr denotes the critical density for the wave length of the pump laser At these high densities, all Raman scattering is forbidden [8], but instabilities like ponderomotive filamentation are strongly boosted [9]. We will investigate and discuss the impact of using non-constant plasma density profiles, as proposed by Riconda et al [28]
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