Imaging of acoustic fields generated in a longitudinal leaky SAW resonator

We utilize a sensitive scanning laser-interferometric probe to map the spatial distribution of the acoustic field within a one-port synchronous leaky longitudinal SAW (LLSAW) resonator. This marks the first visualization of LLSAWs within such a structure. Interest in these waves exists since LLSAWs feature high velocities (>6100 m/s) on the YZ-LiNbO₃ substrate and hence enable the fabrication of bandpass filters operating in the 2.5-5 GHz range with conventional optical lithography. Measurements at frequencies below and above the resonance for a 1.6 GHz LLSAW resonator fabricated on YZ-cut LiNbO₃ are performed. We find that below the resonance frequency the longitudinal profile does not feature a beating pattern typically observed for leaky SAW resonators. The transversal profile within the IDT features 2, 3, 4, 5, ... maxima as the drive frequency is increased. Furthermore, oblique Rayleigh-wave beams are observed to radiate from the sides of the resonator.