  In this methods paper, we explore the capabilities of high-speed ultrasound
imaging (USI) to study fast varying and complex multi-phase structures in
liquids and soft materials. Specifically, we assess the advantages and the
limitations of this imaging technique through three distinct experiments
involving rapid dynamics: the fl ow induced by a liquid jet, the dissolution of
sub-micron bubbles in water, and the propagation of shear waves in a soft
elastic material. The phenomena were simultaneously characterized using optical
microscopy and USI with bubbles as contrast agents. In water, we use compounded
high-speed USI for tracking a multi-phase flow produced by a jetting bubble
diving into a liquid pool at speeds around 20 m/s. These types of jets are
produced by focusing a single laser pulse below the liquid surface. Upon
breakup, they create a bubbly fl ow that exhibits high reflectivity to the
ultrasound signal, enabling the visualization of the subsequent complex
turbulent flow. In a second experiment, we demonstrate the potential of USI for
recording the stability and diffusive shrinkage of micro- and nanobubbles in
water that could not be optically resolved. Puncturing an elastic material with
a liquid jet creates shear waves that can be utilized for elastography
measurements. We analysed the shape and speed of shear waves produced by
different types of jetting bubbles in industrial gelatin. The wave
characteristics were simultaneously determined by implementing particle
velocimetry in optical and ultrasound measurements. For the latter, we employed
a novel method to create homogeneously distributed micro- and nanobubbles in
gelatin by illuminating it with a collimated laser beam.
