Acoustic cavitation in liquids submitted to power ultrasound creates transient extreme conditions inside the collapsing bubbles, which are the origin of unusual chemical reactivity and light emission, known as sonoluminescence. In the presence of noble gases, nonequilibrium plasma is formed. The "hot" particles and the photons generated by collapsing bubbles are able to excite species in solution.
Pflieger, R., Chave, T., Virot, M., Nikitenko, S. I. Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation. J. Vis. Exp. (86), e51237, doi:10.3791/51237 (2014).