An acoustic monitoring method and system in laser-induced optical
breakdown (LIOB) provides information which characterize material which
is broken down, microbubbles in the material, and/or the microenvironment
of the microbubbles. In one embodiment of the invention, femtosecond
laser pulses are focused just inside the surface of a volume of aqueous
solution which may include dendrimer nanocomposite (DNC) particles. A
tightly focused, high frequency, single-element ultrasonic transducer is
positioned such that its focus coincides axially and laterally with this
laser focus. When optical breakdown occurs, a microbubble forms and a
shock or pressure wave is emitted (i.e., acoustic emission). In addition
to this acoustic signal, the microbubble may be actively probed with
pulse-echo measurements from the same transducer. After the microbubble
forms, received pulse-echo signals have an extra pulse, describing the
microbubble location and providing a measure of axial microbubble size.
Wavefield plots of successive recordings illustrate the generation,
growth, and collapse of microbubbles due to optical breakdown. These same
plots can also be used to quantify LIOB thresholds.