Effect of Shape and Asymmetry of Density Ramp on Laser Pulse Amplification Via Stimulated Brillouin Scattering

The amplification of ultrashort laser pulses has attracted significant attention in recent years. An advanced approach involves utilizing plasma as a medium for the amplification process. In this research, we conduct particle-in-cell (PIC) simulations to study the interaction between two counter-propagating seed and pump pulses in a plasma with sub-quarter-critical density. To reduce noise in the simulations, we initially optimized the number of particles per cell. Various plasma conditions affecting the amplification process are considered. The findings reveal that among the studied cases, density ramps and plasma lengths significantly influence energy transfer efficiency. The seed pulse reaches maximum amplification at a plasma density of 0.0104 ner, where the largest Brillouin peak is observed. For the three ramp shapes-linear, quadratic, and exponential-the results show that quadratic ramps achieve the highest amplification levels due to the enhanced phase matching condition. It was also found that seed amplification is more effective with asymmetric density ramps. These insights contribute to the optimization of plasma-based stimulated Brillouin scattering for achieving ultrahigh-intensity laser pulses in applications ranging from inertial confinement fusion to high-energy particle acceleration.