Brillouin Scattering Study of Acoustic Attenuation in Fused Quartz

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.