Brillouin Scattering Study of Acoustic Attenuation in Fused Quartz

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Abstract
The velocity and attenuation of 27-28-GHz longitudinal hypersonic waves in fused quartz have been measured for temperatures between 80 and 600°K. The data are obtained using high-resolution signal-averaging techniques of thermal Brillouin spectroscopy. The velocity, or Brillouin shift, is found to increase with temperature at a rate of ∼0.011%/°K throughout the range. The attenuation, or linewidth, goes through a pronounced peak at a temperature of ∼130°K. This sort of behavior usually indicates a structural relaxation mechanism for the hypersonic damping, as has been suggested for previous ultrasonic measurements in fused quartz. However, it is demonstrated that an anharmonic model involving three-phonon interactions can explain the absorption data with fewer adjustable parameters, which have better physical justification.