Simulation study of enhanced Raman backward amplification in ionizing plasma

Abstract

The Raman backward amplification (RBA) in a plasma is a promising mechanism for the generation of ultrashort, high-energy laser pulses without damaging the amplification medium. However, one limitation of plasma-RBA is the pre-depletion of the pump pulse by Raman backscatter or collisional energy loss due to the thermal noise in the pre-loaded plasma. In this study, we revisit the idea of ionizing plasma by the seed pulse to mitigate the pump energy loss. From one-dimensional particle-in-cell simulations, we obtained approximately four times higher amplification in hydrogen gas, which is ionized by the seed pulse, compared to the same process in a pre-loaded plasma. We observed that the frequency of the amplified seed pulse is significantly down-shifted due to photon deceleration in the wakefield, leading to positive chirping in the amplified seed pulse and its subsequent compression. Overall, these findings suggest that substituting ionizing plasma for pre-loaded plasma can significantly reduce energy loss in Raman backward amplification, enabling the generation of high-energy laser pulses with improved performance. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/4.0/), https://doi.org/10.1063/5.0279646