Optical Mixing in Stimulated Brillouin Spectra*

Optical mixing in 23 liquids and 2 glasses is reported. Observations with a high-resolution grating spectrograph of the light from a giant-pulse ruby laser transmitted through the materials reveal the presence of more Stokes-shifted components than can be accounted for on the basis of amplification by the laser of Brillouin-shifted frequencies. In addition, anti-Stokes-shifted components are observed. The frequency shifts are shown to correspond to those expected for 180° Brillouin scattering. Sound speeds calculated agree in general with those from stimulated and spontaneous scattering experiments. Sound-speed measurements at different temperatures and for two-component liquids give results predictable from bulk properties of the liquids. A number of experiments showing the conditions and the parameters which affect the optical mixing are described.