Description
High-energy laser beams used in inertial confinement fusion (ICF) experiments are subject to phase aberrations as they propagate through numerous optical elements. These aberrations induce large non-uniformities at the focal spot and significant shot-to-shot variations, which can compromise implosion symmetry. While Random Phase Plates (RPP) are routinely employed to improve beam stability, this spatial smoothing technique inherently creates small-scale hot spots known as speckles. These speckles strongly affect laser-plasma interaction by seeding deleterious instabilities, specifically Stimulated Brillouin Scattering (SBS) and Backward Stimulated Raman Scattering (SRS). These processes lead to potential optics damage, target pre-heating via supra-thermal electrons, and a reduction in the energy effectively delivered to the capsule. To mitigate these effects, the speckle coherence time, tc, must be shorter than the growth rate of the instabilities. Currently, standard Smoothing by Spectral Dispersion (SSD) appears insufficient to reach this regime. Using 2D and 3D Particle-In-Cell (PIC) simulations optimized for CPU and GPU architectures, we investigate several schemes to break spatial and temporal coherence in the kinetic regime. We focus on Broadband Laser configurations and the Induced Spatial Incoherence (ISI) method. Our results demonstrate that while reducing SBS is achievable, certain configurations can dramatically increase SRS, highlighting limitations of using "moderate bandwidth" approaches.