Relationship between coherent acoustic wave generation and a coherence spike in an impulsive stimulated Brillouin scattering experiment

Impulsive stimulated Brillouin scattering has been measured for liquid CCl4 and CS2. A spike and an oscillation that are due to the generated acoustic wave are observed. The spike in CCl4 changes its sign when the period of the acoustic vibration is varied, implying interference between these processes. The spike in CS2 is accompanied by a broad component. The peak ratio of the spike intensity to the broad component intensity reaches nearly 5:1 and varies with the pulse duration. When the time interval between the two pump pulses is increased, the spike splits in two, and the acoustic vibration disappears. These results are well described by a third-order nonlinear polarization model that takes account of light-induced acoustic wave generation.