Light emission from collapsing superheated steam bubbles in water

The first observations of light emission accompanying the collapse of supersaturated steam bubbles injected into water are reported. A commercial cappuccino machine provided the steam and the luminescence was observed using a high-gain image intensifier (IIT) microscope system with a spectral response from 380 to 620 nm. A photomultiplier was used to record the light emission as a function of steam and water temperatures. No light was detected at water temperatures above 80–85°C. It was found that each collapsing bubble produces a short-duration light pulse (whose measured duration was limited by the electronics used) which was accompanied by a coincident sound pulse (recorded by a hydrophone). Limited spectral measurements indicate a substantially flat spectrum in the measured range (400–600 nm). Parallels are noted between the vapour bubble luminescence and conventional single-bubble sonoluminescence.