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: $c_{11}=10.764\mathrm{}\pm 0.002$, $c_{12}=1.252\mathrm{}\pm 0.023$, and $c_{44}=5.774\mathrm{}\pm 0.014$ 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: $p_{44}=-0.172\mathrm{}$ and $p_{11}-p_{12}=-0.292\mathrm{}$ determined by Denning et al. and $p_{11}+2\mathrm{}{p}_{12}=-0.1640\mathrm{}$ 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., $\mathrm{}\left|a\right|=4.4\mathrm{}\pm 0.3$ ${\mathrm{\AA }}^2$.