Nematic Brillouin scattering

A direct confirmation of the existence of these two branches has been found by Liao, Clark and Pershan from their Brillouin scattering experiments on a monodomain sample of jff-methyl butyl /K(p-methoxy-benzylidene)amino) cinnamate. This compound shows the nematic, smectic A and smectic B phases. Choosing both the incident and the scattered light to be polarized either as ordinary or extraordinary waves, they observed two peaks corresponding to the two modes, the angular dependence of which is in excellent agreement with the theory (fig. 5.3.11). 

Brillouin scattering from the nematic (racemic) lyotropic polymer poly-y-benzyl glutamate (PBG) shows a significant anisotropy in both the sound velocity (22%) and the Brillouin linewidth (40%) in the solutions [22], when measurements are made at different angles with respect to the nematic director. Figure 4 shows typical Brillouin spectra of PBG as a function of scattering angle. This work indicates the importance of elastic relaxations due to concentration fluctuations in these nematic polymeric materials. 

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