Brillouin sound attenuation

Above about 0.5 GHz, Brillouin scattering provides an elegant technique of measuring phonon mean free paths (which are inversely proportional to the sound attenuation coefficient) by evaluating the width of the Brillouin lines [53]. However, as a result of finite spectrometer resolution and contrast, this method is limited to aerogel densities above 180 kg/m. ... 

The width, r, (half width at half maximum) of the Brillouin lines is proportional to the sound attenuation coefficient. 

Here, we briefly summarize the results for the dynamic structure factor. The dynamic sfiucture factor exhibits three peaks, a central Rayleigh peak caused by the thermal diffusion, and two symmetrically placed Brillouin peaks caused by sound. The width of the central peak is determined by the thermal diflfusivity, Dj, while that of the two Brillouin peaks is related to the sound attenuation coefficient, r. For the SRD algorithm [57],... 

Fig. 5. Polarized Rayleigh-Brillouin spectrum of amorphous PnHMA taken with a Burleigh plane Fabry-Perot interferometer using a free spectral range of 12.4 GHz at 295 K. The two Brillouin peaks are shifted from the incident frequency by the product of the wave vector q and the sound velocity u. The line width of the Brillouin peaks is related to the attenuation of the sound waves. PnHMA.

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