In addition to the classical fundamental thickness mode, multiple echoes of Lamb waves have been observed on pulsed circular piezoelectric transducers, by using an optical heterodyne interferometer. With an efficient resonance spectrum technique, the group velocities of the Lamb waves are deduced quantitatively. The radiation of these waves into liquids (usually water), which create so called ‘‘head waves’’ and are not predicted by the piston model, were detected by a hydrophone. Comparison between the optical and hydrophone probe measurements demonstrates a good agreement.