Effects of frequency-modulated pump on stimulated Brillouin scattering in inhomogeneous plasmas

The effects of a frequency-modulated pump on stimulated Brillouin scattering (SBS) in a flowing plasma are investigated by theoretical analysis, three-wave simulations, and kinetic simulations. The resonance point of SBS oscillates in a certain spatial region with time when frequency modulations are applied. There exists a certain frequency modulation that causes the velocity of resonant points to be similar to the group velocity of the seed laser, which increases the SBS reflectivity. The SBS can also be suppressed by frequency modulation with larger bandwidth. In the kinetic simulations, the effects of the frequency-modulated pump on the reflectivity agree with our theoretical predictions. Multi-location autoresonance is also observed in the narrow-bandwidth frequency modulation case, which can also increase the SBS reflectivity. Our work provides a method for selecting the laser bandwidth to inhibit SBS in inhomogeneous plasmas.