What Is Sonoluminescence?

When intense sound waves pass through a liquid, they create alternating high and low pressure zones. During the low-pressure phase, dissolved gas forms tiny bubbles (cavitation). During the high-pressure phase, these bubbles collapse with extraordinary violence. Single-bubble sonoluminescence (SBSL), first stably achieved in 1989 by Felipe Gaitan, involves trapping a single bubble in a standing sound wave and observing it emit a flash of light with each acoustic cycle — about 30,000 flashes per second, each lasting less than 100 picoseconds (trillionths of a second). The collapsed bubble reaches temperatures estimated at 20,000-100,000 Kelvin and produces light across the visible and UV spectrum. The exact mechanism of light emission remains debated: thermal bremsstrahlung (radiation from extremely hot plasma), quantum vacuum effects, and shock wave models have all been proposed. The phenomenon concentrates sound energy by a factor of roughly 10^12 into a tiny volume, representing one of the most extreme energy-focusing processes known.