Kinetic simulations of record-efficiency Raman amplification experiments at LLE

Stimulated Raman backscatter in plasmas presents a promising route for amplifying high-power laser pulses in compact systems. While theoretical and computational studies have highlighted the potential for Raman amplification to achieve high efficiencies, laboratory experiments have historically fallen short of expectations.

Recent experiments at the University of Rochester’s Laboratory for Laser Energetics (LLE) have achieved record Raman energy transfer efficiencies, exceeding 8%. This result was critically enabled by the use of a high-intensity seed pulse, which allowed the amplification of the seed to promptly enter into the nonlinear pump-depletion regime.

In this work, we present fully kinetic, particle-in-cell (PIC) simulations that elucidate the physics underlying the recent LLE Raman amplification experiments. We show that simulations reproduce energy transfer efficiencies comparable to those measured in the laboratory. We identify wavebreaking of the electron plasma wave as a key limiting mechanism for further energy transfer, and reveal the important interplay between Raman forward and backscatter on the evolution of the amplified seed.