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 (ITT) microscope system with a spectral response from 380 to 520 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 degreesC. 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. (C) 2001 Elsevier Science B.V. All rights reserved.