Optical diffraction studies of sound waves in lithium niobate

The acousto-optic interaction in the Raman-Nath regime was used to study sound waves propagating in the principal planes of piezoelectric lithium niobate. Complete cuts of the inverse phase velocity surfaces were obtained for surface waves on reflection and for three bulk waves and one surface wave on transmission through the surface acoustic wave (SAW) propagation surface. It is also shown how simple diffraction can be used to measure the group velocity direction and the electro-mechanical coupling coefficient for surface waves. A modified schlieren technique was used to visualize bulk waves generated by a finite transducer and to observe shear waves reflecting and mode converting to longitudinal waves at an interface.