Laser probe investigation of leaky surface waves on 41° and 64°-LiNbO3+

This paper presents the first reported laser probe measurements of leaky SAW propagation on both 41° and 64° rotated-Y X-propagate lithium niobate substrates. A conventional specular reflection based Rayleigh wave laser probe is used in conjunction with standard signal processing techniques. The laser probe detects the net vertical surface motion on the SAW substrate where both Rayleigh and leaky SAW components are present. This motion can also be contributed by bulk waves that are reflected from the bottom of the substrate. These components are resolvable in the time domain owing to their different time-of-arrival when a stationary probe spot is placed at a distance away from the launching transducer. Their identification can also be verified by examining the corresponding time-gated frequency domain responses. The on-axis propagation velocity of the Rayleigh and leaky wave components as well as additional evolutionary behavior are obtained by probing along the principal SAW propagation path. One example is the direct confirmation of a secondary propagation path in both substrates. This path results from radiation into the bulk that is in turn reflected from the bottom surface of the substrate and, upon reaching the top surface, regenerates both leaky and Rayleigh waves. A second example is the quantitative determination of the leaky wave stopband as well as the leaky-Rayleigh scattering stopband in a reflection grating structure. Also, longitudinal profiles measured from leaky wave based 1-port SAW resonator allowing possible deduction of propagation attenuation inside the stopband and the dispersion curve are presented