We report time-resolved measurements of the phase of the Stokes beam produced by stimulated Brillouin scattering in gases. We observed phase jumps, slow phase drifts, and sudden frequency shifts during the temporal evolution of individual Stokes pulses. Phase jumps, and the intensity variations that accompany them, are macroscopic manifestations of the noise that initiates and sustains stimulated scattering.

• Received 30 October 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.1702