Quasielastic Light Scattering from Diamond

Strong quasielastic features have been found in light scattering from diamond in the frequency range 0 to ± 200 GHz and have been investigated as a function of wave-vector transfer ($Q$) and temperature ($T$). The evolution of a relatively narrow Lorentzian component (∼ 10 GHz) demonstrates for the first time the manner in which a two-phonon difference spectrum in the collision-free regime (low $T$ and large $Q$) develops into entropy-fluctuation scattering in the collision-dominated regime (high $T$ and low $Q$).