Simulations of drastically reduced SBS with laser pulses composed of a Spike Train of Uneven Duration and Delay (STUD pulses)

TL;DR

This paper demonstrates through numerical simulations that STUD pulses significantly reduce parametric instability growth in laser-produced plasmas compared to traditional smoothing techniques, by minimizing plasma wave re-amplification.

Contribution

It introduces STUD pulses as a novel laser pulse shaping method that drastically suppresses SBS instability growth in plasma simulations.

Findings

STUD pulses reduce SBS instability growth by orders of magnitude.

Frequent speckle pattern changes keep ion acoustic wave levels low.

STUD pulses outperform RPP and SSD in suppressing plasma instabilities.

Abstract

By comparing the impact of established laser smoothing techniques like Random Phase Plates (RPP) and Smoothing by Spectral Dispersion (SSD) to the concept of "Spike Trains of Uneven Duration and Delay" (STUD pulses) on the amplification of parametric instabilities in laser-produced plasmas, we show with the help of numerical simulations, that STUD pulses can drastically reduce instability growth by orders of magnitude. The simulation results, obtained with the code {\sc Harmony} in a nonuniformly flowing mm-size plasma for the Stimulated Brillouin Scattering (SBS) instability, show that the efficiency of the STUD pulse technique is due to the fact that successive re-amplification in space and time of parametrically excited plasma waves inside laser hot spots is minimized. An overall mean fluctuation level of ion acoustic waves at low amplitude is established because of the frequent change of the speckle pattern in successive spikes. This level stays orders of magnitude below the levels of ion acoustic waves excited in hot spots of RPP and SSD laser beams.