A TIME-RESOLVED X-RAY-DIFFRACTION STUDY OF HOT PHONONS IN QUARTZ

We have performed a time-resolved x-ray diffraction study of hot (non-equilibrium) phonons in alpha-quartz at low temperatures. The phonon generation mechanism is direct stimulation of transverse-optical (TO) phonons by infrared light excitation using a powerful Q switched CO2 laser with the intent of possibly understanding how the excited system then approaches equilibrium. Also we hoped to demonstrate that time-resolved x-ray scattering can give useful information on the time and spatial evolution of this path to equilibrium. We have observed temporal diffuse scattering peaks at various wavevectors which confirm the presence of non-equilibrium phonons generated by the initial laser excitation. We have observed the zone center TO phonons directly excited by the laser pulse. Some of the later diffuse scattering peaks have been identified as acoustic phonon decay products, while other peaks have not yet been identified. Possible origins of these peaks are given.