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

Abstract

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 x 10⁻⁵), several noise reduction schemes were used to enhance the signal to noise ratio. The spectrometer was evaluated by studying the strongly scattering liquid CS₂ and the weakly scattering liquid CC1₄. 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 CC1₄ we were able to observe the so-called Mountain mode and to confirm that CC1₄ can be modeled as a liquid exhibiting a single relaxation time.