Direct observation of surface acoustic wave interaction with a phononic crystal

Heterodyne laser interferometer has been used to directly study surface acoustic wave interaction with a twodimensional phononic crystal. Acoustic waves are launched by interdigital transducers towards a square lattice of holes etched into the piezoelectric substrate. Interferometer measurements performed at frequencies below, within and above the expected band gap frequency range provide direct observation of the wave interaction with the phononic crystal, revealing anisotropic scattering into higher diffraction orders depending on the apparent grating pitch at the boundary between the phononic crystal and free surface. Furthermore, the measurements also confirm the existence of an elastic band gap, in accordance with previous electrical measurements and theoretical predictions.