Phonon attenuation in amorphous solids studied by picosecond ultrasonics

We have used a picosecond optical technique to measure the attenuation alpha of longitudinal-acoustic phonons in several disordered solids. We find a universal alpha similar to nu(2) behavior for frequencies v up to 320 GHz and for temperatures between 80 and 300 K. Within this temperature range the phonon attenuation increases by a factor of between 2 and 3 with increasing temperature for the amorphous polymers poly(methyl methacrylate), poly(styrene), and poly(ethyl methacrylate), and for the metallic glass TiNi. We discuss our results in relation to current theories of high-frequency vibrations in glasses and thermal conduction.