  The acoustic modes of diamond not only are of profound significance for
studying its thermal conductivity, mechanical properties and optical
properties, but also play a determined role in the performance of
high-frequency and high-power acoustic wave devices. Here we report the bulk
acoustic waves (BAWs) and surface acoustic waves (SAWs) of single crystal
diamond by using the angle-resolved Brillouin light scattering (BLS)
spectroscopy. We identify two high-velocity surface skimming bulk waves, with
sound velocities of 1.277x10^6 and 1.727x10^6 cm/s, respectively. Furthermore,
we conduct the relationship among the refractive index, incident angle and the
velocities of BAWs propagating along an arbitrary direction. Our results may
provide a valuable reference for fundamental researches and devices engineering
in the community of diamond-based acoustic study.
