Send a high-intensity ultrasound wave through a container of liquid, and it’s not surprising to find that the alternating cycles of acoustic compression and rarefaction create micron-sized bubbles in the liquid and cause them to successively expand and contract. What is mysterious is to see those bubbles emit light. Somehow, the energy dispersed in an acoustic wave-field becomes sufficiently concentrated to produce visible light.
Multiple-bubble sonoluminescence (MBSL) was first seen in the 1930s, but in recent decades researchers have learned to produce and control a stable single bubble. Single-bubble sonoluminescence (SBSL) has allowed them to study in detail the dynamics of bubble cavitation. Experiments soon revealed other remarkable features: The bursts of light are as short as a few tens of pico-seconds and the time between successive pulses can be synchronized to within a few parts in 1011. (See the articles in Physics Today, by Lawrence A....
