Short-pulse amplification by strongly coupled stimulated Brillouin scattering

Abstract

We examine the feasibility of strongly-coupled stimulated Brillouin scattering as a mechanism for the plasma-based amplification of sub-picosecond pulses. In particular, we use fluid theory and particle-in-cell simulations to compare the relative advantages of Raman and Brillouin amplification over a broad range of achievable parameters.

X-ray amplification by stimulated Brillouin scattering

“…The linear growth rate of the undamped system represents the early-time behavior of the interaction and is important for quantifying the highest degree of amplification that may be expected. It can be shown that the undamped asymptotic seed growth rate in the linear regime is simply the instability plane-wave growth rate, for which expressions are well known for SRS, WC-SBS, and SC-SBS and which may be readily calculated for in-termediate SBS conditions [37]. In Fig.…”

“…(a * 1 a 2 ) (A13) which reduces to the strongly-coupled and weaklycoupled limits, as described in Ref. [37], if the secondorder or first-order time derivatives are neglected, respectively.…”

“…When the resonance conditions for counterpropagating beams * mredward@princeton.edu † j.mikhailova@princeton.edu ‡ fisch@princeton.edu are approximately met (ω 2 = ω 3 + ω 1 , k 2 = k 3 − k 1 ), energy is efficiently transferred from the pump to the seed beam, resulting in amplification and compression of the seed pulse to up to relativistic intensities and plasma-wave-period durations [36]. Since the Langmuir wave has a shorter period than the ion-acoustic wave, Raman amplification tends to give higher growth rates, more intense amplified pulses, and shorter pulse durations [37], and SRS has been studied in greater depth [38][39][40][41][42][43][44][45][46][47][48][49][50]. However, because SBS allows the pump and seed to be at almost the same wavelength, it has been considered as an alternative to SRS in both the weaklycoupled regime (WC-SBS), where the plasma mode is the ion acoustic wave [51,52], and the strongly-coupled regime (SC-SBS), where the plasma response is a driven ion quasi-mode [53][54][55][56][57][58][59][60][61][62].…”

“…However, because SBS allows the pump and seed to be at almost the same wavelength, it has been considered as an alternative to SRS in both the weaklycoupled regime (WC-SBS), where the plasma mode is the ion acoustic wave [51,52], and the strongly-coupled regime (SC-SBS), where the plasma response is a driven ion quasi-mode [53][54][55][56][57][58][59][60][61][62]. For Brillouin amplification it is often necessary to consider both the strongly and weaklycoupled contributions [37,63], as well as the distinction between SRS and SBS [64]. Particle-in-cell (PIC) simulations have also suggested that SBS performance improves in a slightly collisional plasma [65].…”

“…where a 0 is the pump field strength (a 2 ) before interaction. The Brillouin growth rate may be evaluated numerically in the intermediate regime [37], with the weak and strong coupling limits [71]: Lnd.…”