Acoustic phonon dispersion measured with time-resolved X-ray diffraction

Summary form only given. Acoustic phonon dispersion was measured in a Ge single crystal using time-resolved X-ray diffraction. The experiments reported here were conducted at the Advanced Photon Source. An undulator/cryogenically cooled Si monochrometer pair produced 10 keV X-rays for the experiment. A commercial Ti:sapphire 840 nm, 70 fs, 1 kHz laser system was phase locked to the electron bunches in the storage ring. The laser was used to impulsively excite a two side polished Ge [100] single crystal. The absorption of the ultrafast optical light on the crystal surface generates a coherent acoustic pulse. The symmetric 400 diffraction plane was used to diffract the X-rays. The time-resolved X-ray detector was an avalanche photodiode.