PHONON INTERACTIONS IN CRYSTALS

Additional experimental work was done on the parametric up-conversion process in a variety of crystals and along different axes (see AD-601 093). These crystals include MgO, Ge, Al2O3, quartz, and CaF2. These measurements allow an evaluation of the size of the third order (anharmonic) constants. Theoretical work was also done on the inter-relationships between these collinear forward travelling wave processes and the attenuation of microwave acoustic beams by interaction with the thermal phonon distribution. Rather large interactions between the microwave phonons and the conduction electrons in samples of germanium were observed. More data was obtained on the temperature variation of the microwave phonon attenuation and these data were related to the anharmonic potential constants derived from the work on parametric up-conversion. Among other activities, an investigation of more rigorous solutions of time dependent problems in non-linear elasticity theory was begun. Also, thin film CdS transducers were operated at 9 Gc/sec. A report on the transmission of heat pulses is also included.