Sonoluminescence

Sonolumescence, or sonoluminescence, is the emission of short bursts of light from a collapsing gas bubble in a liquid when driven by a strong acoustic field. The phenomenon was first observed in 1934 by Frenzel and Schult during ultrasonic cavitation, and has since been studied extensively for insights into high-temperature physics and bubble dynamics.

In the typical single-bubble setup, a gas-filled bubble trapped in a standing ultrasonic wave is driven to oscillate. During the low-pressure phase the bubble grows, and as the pressure reverses it collapses violently, compressing the gas within to extreme temperatures and pressures, producing a flash of light lasting on the order of tens to hundreds of picoseconds. The light is detected with photomultiplier tubes or fast cameras, and can be synchronized with the acoustic drive.

Spectral characteristics indicate a broad continuum, often interpreted as thermal emission from a hot plasma with estimated temperatures ranging from a few thousand to tens of thousands of kelvin. However the exact mechanism remains debated, and the temperatures inferred from simplistic models can be uncertain. The dynamics are typically described by Rayleigh–Plesset-type hydrodynamics; additional chemical and plasma processes may contribute.

Separating single-bubble from multi-bubble sonolumescence, the latter occurs in bubbly liquids with many coexisting bubbles, producing less coherent light. The field has driven interest as a potential ultra-fast light source and as a probe of cavitation and extreme states of matter, though practical applications remain limited.