Double-transducer structure for picosecond ultrasound generation

Abstract

We report a double-transducer technique for more effective generation of picosecond acoustic waves. A tungsten layer, which is buried under a transparent film and a thin top metal transducer, plays the role of a bottom laser-acoustic transducer as well as a high-impedance acoustic reflector. The pulse shape and the induced piezoreflectance response of the acoustic wave launched by the bottom transducer are different from the conventional top transducer. The effect of the bottom transducer depends on the thicknesses and optical constants of the top transducer and the transparent film. The accuracy of velocity measurement can be raised owing to more efficient energy utilization, halved pulse broadening and attenuation of the tungsten-launched waves, and the added signatures on the reflectance curve.