Raman spectra of diamond at high pressures

The first-order Raman spectrum of diamond has been measured in a diamond-anvil cell up to 27 GPa. The fundamental phonon line varies linearly in pressure with a shift of 2.87 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/GPa. This line appears to be an excellent pressure-calibration standard as an alternate to the ruby pressure scale.