Three-dimensional wave propagation simulations and experiments show that the gain exponent, an often used metric to assess the likelihood of stimulated Brillouin scatter, is insufficient and must be augmented with another parameter, $N_r$, the ratio of the resonance length, $L_{\text{res}}$, to the laser speckle length. The damping rate of ion acoustic waves, $\nu$, and thus $L_{\text{res}}$, which is proportional to $\nu$, are easily varied with plasma species composition, e.g., by varying the ratio of hydrogen and carbon ions. As $N_r$ decreases, stimulated Brillouin scattering increases despite the same gain exponent.

• Received 13 November 2014

DOI:https://doi.org/10.1103/PhysRevE.91.031103