Ultrasound characterization of cavitation microbubbles produced by femtosecond laser pulses

An ultrasound-based technique capable of detection and spatio-temporal characterization of microbubbles induced in water by femtosecond laser is reported. A highly focused single-element ultrasound transducer was used both to detect passive acoustic emission of the microbubbles and to probe the microbubbles at different stage of their evolution. The location of origin and wall of the microbubble was assessed from temporal characteristics of the passive acoustic emissions and of the pulse-echo signals. The radius of the microbubble was estimated as the distance between the origin of the bubble and its wall. The ultrasound characterization of microbubbles induced by femtosecond pulses agreed well with theoretical predictions based on the well-known Rayleigh-based model of bubble behavior in liquid. The results of this study demonstrate that femtosecond laser-induced microbubbles with typical sizes of several tens of micrometers can be characterized by the developed ultrasound technique.