Abstract: An acousto-optical device includes a solid state substrate having optical characteristics affected by an acoustic wave in the substrate, and a Z-cut lithium tantalate transducer coupled to the substrate for inducing the acoustic wave. Lithium tantalate provides the transducer with a coupling coefficient and acoustic impedance mismatch which generate a very high finesse acoustic standing wave within the substrate. The lithium tantalate also provides low shear wave components with relatively high manufacturing tolerances. The acousto-optical device with a lithium tantalate transducer is also utilized as a high Q modelocker in a laser capable of producing short pulses of laser light.