Sonoluminescence research. Scientist with equip- ment for researching sonoluminescence, the produc- tion of light from bubbles in water when exposed to high-frequency sound (ultrasound). The resear- cher is injecting tiny bubbles into a bulb filled with water that has no gas dissolved in it. The bubbles are trapped at the centre of the bulb by ultrasound that makes them expand and contract. As the bubbles collapse on themselves at speeds of more than 4 times the speed of sound in air, a shock wave is created within them which concentra- tes enough energy to create a pulse of light that lasts for 50 microseconds. Photographed at the Meurice Institute in Brussels, Belgium.