'Water Hammer' power

At the Acoustical Society of America in Nashville, Seth Putterman of UCLA described a new 'water hammer' method for generating sonoluminescence (SL),.the transformation of sound into light.

This approach yields SL flashes with higher powers than in the ordinary SL process. With the ordinary system a sound wave enters a liquid tank, and produces bubbles that collapse and release ultra-short flashes of light. In the water hammer version, researchers shake a 20" long, 1.5" diameter cylindrical tube with a force of 2 g's.

Filled with water and a small amount of xenon gas, the tube shakes so that water in each half of the tube travels in an opposite direction and temporarily creates a wave that generates SL in the water, producing an output of approximately 300 million photons that add up to a peak power of about half a watt.

The scaled-up photon output, Putterman says, makes it possible to perform more and better measurements of the hard to understand SL phenomenon.

In a separate experiment that uses the traditional approach of aiming sound at a liquid tank, Putterman and colleagues have successfully achieved SL with 1 MHz sound waves, as opposed to the 20-40 kHz waves that are conventionally used.

While MHz sound waves are currently used in various acoustics applications, megahertz SL from a single bubble has not been achieved before.