Brillouin scattering in diamond

The Brillouin spectrum of diamond excited with either the ${\mathrm{Ar}}^{+}$ or He-Ne laser radiation is measured with a triple-passed piezoelectrically scanned Fabry-Perot interferometer. The polarization features and the selection rules have been verified for a number of scattering geometries. From the measured frequency shifts of the Brillouin components, the following values are obtained for the elastic moduli: ${c}_{11}=10.764\ifmmode\pm\else\textpm\fi{}0.002$, ${c}_{12}=1.252\ifmmode\pm\else\textpm\fi{}0.023$, and ${c}_{44}=5.774\ifmmode\pm\else\textpm\fi{}0.014$ in units of ${10}^{12}$ dyn/${\mathrm{cm}}^{2}$. The relative intensities of the observed Brillouin components for a variety of scattering geometries are consistent with the following elasto-optic contants: ${p}_{44}=\ensuremath{-}0.172$ and ${p}_{11}\ensuremath{-}{p}_{12}=\ensuremath{-}0.292$ determined by Denning et al. and ${p}_{11}+2{p}_{12}=\ensuremath{-}0.1640$ obtained by Schneider. From a comparison of the Brillouin spectrum and the Raman spectrum associated with the zone-center optical phonon, observed under identical conditions, we obtain a value for the single independent component characterizing the Raman tensor per unit cell, viz., $|a|=4.4\ifmmode\pm\else\textpm\fi{}0.3$ ${\mathrm{\AA{}}}^{2}$.