Observation of highly nonlinear surface-acoustic waves on single crystal lithium–niobate plates by means of an optical sampling probe

A new type of laser probe for observation of surface-acoustic waves (SAWs) is presented. The probe operation is based on the knife-edge technique combined with an optical sampling method that employs a pulsed laser beam. The spatial resolution of the probe is 1.3 μm and its bandwidth is greater than 1 GHz. A highly nonlinear SAW involving 10 harmonics on single-crystal lithium-niobate (LiNbO3) plates has been studied at the input frequency 200 MHz. It is shown that the initially sinusoidal wave breaks into a train of pulses up to four per period with the evolution of time. The spectrum data were related to SAW harmonic generation studied previously under similar conditions. Head-to-head collision of two SAW wave packets of 500 ns duration has been studied. It was confirmed that the wave forms are preserved in the collision. In addition, the effect of nonlinear diffraction of a SAW driven by high input power levels was observed. The present probe is found to be a powerful tool for elucidation of SAW solitons.