Ultrasonic Study of Three-Phonon Interactions. II. Experimental Results

The intersection of two pulsed ultrasonic beams in isotropic solids is described as an experimental technique capable of yielding direct evidence of certain three-phonon interaction effects. It is shown that a third beam of reasonable intensity is generated at the volume of interaction only when energy and momentum are conserved between the three beams. Polarization effects and beam intensity relationships are in agreement with theoretical predictions. The four-phonon interaction is also examined by ultrasonic techniques, and the process is shown to be much weaker than the three-phonon interaction.