3-DIMENSIONAL SIMULATIONS OF STIMULATED BRILLOUIN-SCATTERING WITH FOCUSED GAUSSIAN BEAMS

We report on a detailed investigation of the process of SBS with focus ed Gaussian beams via a three-dimensional simulation of the SBS proces s that includes spontaneous noise. We show that spontaneous noise pres ent at points other than where tile initiation of SBS occurs does not significantly affect the Stokes wave. The effects on the Stokes beam o f modes not present in the pump wave (nonconjugate modes) are investig ated and it is found that the phase of a given Stokes mode is affected by the presence of other modes, a process termed phase pulling. We al so show that for a focused Gaussian beam the Brillouin gain parameter does not increase linearly with increased pump power once SBS threshol d is reached; rather, above threshold the SBS process resembles a reve rse saturable absorber for the pump wave at any point between the entr ance to the medium and the focal point of the pump beam.