There’s all sorts of physics attached to this that I very much don’t understand, but basically, the principle is that when exposed to sound air bubbles in liquid slowly expand and then contract suddenly and implode, releasing a picosecond burst of light.*
The phenomenon was first recorded in Cologne in 1934, but because of the lack of technology to study it, it was 1989 before any real advancements were made in the field. Some new theories about this involve the science of black holes which is going way, way, way, way, way, way, way outside my sphere of comprehension.**
Personal aside: I know at this point, if you’ve been reading along for a while, you must think that secretly I’m dating a physicist because there is no other reason for which physics should appear in this space so often when I have asserted that the subject was, for over a decade, my sworn enemy. This is not entirely wrong, but not entirely true; two of my very favourite guys in the world are physicists and I tend to pick things up from them whenever I get to talk to them. It is really on them and their patience and willingness to teach a physics moron, that the subject shows up so often.
*Thus the sono part and the luminescence part.