Imaging GHz Surface Acoustic Waves on A Phononic Crystal Island

We use an ultrafast optical technique to examine how point-generated surface acoustic waves travel through a two-dimensional phononic crystal designed as a square lattice pattern of holes within a silicon base. We obtain images at fixed frequencies and analyze the acoustic dispersion. At specific frequencies we observe mode conversion, refraction and beam splitting at the boundary where the structured phononic crystal meets the unstructured silicon base. We also present details of the acoustic dispersion relation.