Brillouin Amplification with a Flying Focus*

Strongly-coupled Brillouin backscattering in plasma is a promising route towards the amplification of high-intensity laser pulses in compact systems. However, to ensure the production of high-quality beams, Brillouin amplification schemes require the control of parasitic effects like pre-heat of the plasma by the pump beam, filamentation of the pump and probe beams, as well as other competing instabilities. Advances in the production and modeling of laser pulses with complex spatio-temporal structure, such as beams with a flying focus, offer new strategies to control these issues.

In this work, we perform multidimensional simulations of Brillouin amplification with a flying focus pump beam using the particle-in-cell code OSIRIS. We show that the use of a flying focus can effectively mitigate the development of premature instabilities triggered by the pump before it interacts with the probe beam. Further, we explore deviations from established nonlinear theory of Brillouin amplification in this new regime, and report on its impact on efficiency and beam quality. We perform parameter scans with different flying focus pump beam properties and plasma conditions and identify the optimal range of parameters for efficient Brillouin amplification with flying focus beams.