Text: [PHYS] When studying the action of ultrasonic waves on the development of photographic plates, Marinesco and Trillat, in 1933, accidentally discovered traces of new latent images in silver halide emulsions on the plates immersed in water. They explained the action as due to the ultrasonic waves accelerating the processes of reduction which are taking place in the sensitive plate by the violent mixing of the reactants, by Frenzel and Schultes, who made similar experiments, believed that the effect was actually due to exposure to light. Sonoluminescence is always accompanied by cavitation, and can be easily seen by the naked eye in a dark room if glycerine is cavitated by the velocity transformer attached to a 20-W, 20-kHz magnetostrictive transformer. It appears as a bluish-white light. Usually the sonoluminescence is so weak that photomultiplier tubes are used to detect it. This led to the discovery that the light appears as discrete flashes which are periodic with the sound field. Work then proceeded to find out at what phase of the sound field, or volume of the cavitating bubbles, the flashes occurred. The definitive experiment on this was performed by Meyer and Kuttruff in 1959. They produced cavitation bubbles on the end face of a nickel rod magnetostrictively excited at 2.5 kHz. At this frequency the bubbles were large and they used the sonoluminescence flash to produce a voltage pulse which activated a flashlight. The end surface of the nickel rod was thus illuminated, and by delaying the activating pulse by various amounts, a series of photographs showing the life cycle of the cavitation bubbles was obtained. These photographs showed clearly that cavitation bubbles started to appear halfway through the sound period, grew to maximum and collapsed rapidly. The sonoluminescence flash occurred at the end of the collapse.

See Also: LUMINIFEROUS ETHER, LIGHT, NOUS, CHEMILUMINESCENCE

Source: 105