Mitigation of stimulated Raman side scattering via spatio-temporal incoherent laser beams

Stimulated Raman side scattering (SRSS) is recently observed in various experiments at ignition relavant conditions by detecting from unexpected scattering directions, which challenges the existing scattered light diagnotics. SRSS could be mitigated by spatio-temporal incoherent laser beams. Continuous phase plate (CPP) creates spatial incoherence via forming multiple speckles. The speckles break the transverse pump field into small structures with the size of diffraction limit, which is hard to trigger SRSS in a single speckle. However, multiple speckles could collectively excite SRSS by seeding side scattered light and hot electrons in strong speckles. Further increasing the spatial incoherence with smaller F number could mitigate the collective effects. Smoothing by spectral dispersion (SSD) introduces temperal incoherence with a frequency bandwidth. As the frequency bandwidth increases, the SRSS could be mitigated efficiently. In combination of CPP with small F number and SSD with Δω>1%, SRSS is shown to be well suppressed.