GHz ultrasound wave packets in water generated by an Er laser

Abstract

A variety of schemes are presented, suitable for the temporally and spatially controlled generation of ultrasound pulses with a centre frequency near 1 GHz. Direct excitation of acoustic waves in water, serving as the coupling and transport medium, relies on the resonant absorption of short erbium laser pulses in water: at the interface with an adjoining solid material or at a free water surface. Ultrasonic amplitudes, leading to nonlinear acoustic effects, have been demonstrated. The photoacoustic excitation methods presented here are suitable for scanning acoustic microscopy, for example for the real-time study of biological cells in vivo.