We've all seen laser beams - narrow and powerful beams of light used in everything from CD players to weapons. Now researchers have found a way to make sound waves that, like light waves in a laser, travel in step. They call it a phaser and it could open up applications as wide-ranging as precision timer circuits and better ultrasound scans.
The researchers from NTT Basic Laboratories in Japan call their device a phaser because it uses phonons, waves of sound that require a medium, such as a gas, liquid or solid, to travel.
To create the beam, they started with a tiny drum just a few nanometers across, and put it inside a cavity, which acted like a resonator. They vibrated the drum, which transmitted energy to the cavity, and created the phonons. The cavity confined the sound waves. At a certain frequency, called the resonant frequency, the material of the cavity relaxed in a very specific way, creating vibrations that transferred energy back into the drum. Those vibrations are at a specific frequency and if one connected the resonator to a solid material those vibrations would travel away in a narrow beam. That traveling wave is the "laser" sound beam. Since the sound waves are all in step with each other, they would go in straight lines and wouldn't spread out.