A Brillouin gain spectrometer and its evaluation by the study of some liquids

The construction and testing of a Brillouin gain spectrometer is discussed. The spectrometer employs a high power (150 mW) tunable dye laser and a low power (1.7 mW) stabilized HeNe laser in a pump-probe arrangement. Because of the small signal gain (1 {dollar}times{dollar} 10{dollar}sp{lcub}-5{rcub}{dollar}), several noise reduction schemes were used to enhance the signal to noise ratio. The spectrometer was evaluated by studying the strongly scattering liquid CS{dollar}sb2{dollar} and the weakly scattering liquid CCl{dollar}sb4{dollar}. Brillouin shifts and linewidths were accurately determined for both liquids. The high resolution of this instrument permitted measurement of the small asymmetry in the measured lineshapes. In CCl{dollar}sb4{dollar} we were able to observe the so-called Mountain mode and to confirm that CCl{dollar}sb4{dollar} can be modeled as a liquid exhibiting a single relaxation time.