Noncollinear Attenuation of Transverse Acoustic Waves inAl2O3

Abstract

For transverse waves propagated along an even-fold axis, the phonon-phonon coupling parameters are zero for collinear interactions. This necessitates a consideration of the angular dependence of the coupling parameter. The angle at which these parameters peak affects the minimum energy deficit possible on interactions. A calculation including both the angular dependence of the coupling parameters and the uncertainty of phonon energy due to thermal-phonon lifetimes is done for the case of A1203 along the a axis. The calculated attenuation fits the experimentally observed attenuation.

Phonon - Phonon Interactionsecond Sound in Solids : The Effects of Collinear and Non-Collinear Three Phonon Processes

“…Neither of these complementary descriptions is, however, able to account satisfactorily for the narrow puke widths observed in NaF, and it is tempting to make comparison with the narrowing of ballistic pulses observed at lower temperatures [18]. If small angle scattering predominates the crystal symmetry may play an important role [19].…”