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Sound Waves Focused Into Laserlike Beam

A beam of sound could usher in new kinds of imagers and super-precise clocks. ->

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.

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Right now the device is confined to a circuit a half an inch on a side. And it can't send out beams of sound over a distance, like the sonic weapons used in crowd control or against Somali pirates. That's because in order for phonons to travel, they need the gas, liquid or solid they're moving through to be consistent that entire way.

Although the word "phaser" is used to mean a laser-like weapon on the science fiction television show and movie Star Trek, it doesn't mean that here. But like lasers, phasers end up in common use. For example a resonator could translate the beams of phonon vibrations into electrical signals, replacing the quartz crystals currently used in watches and clocks. And the high frequencies mean that it could provide a better picture than current ultrasound systems.

The work appears in the journal Physical Review Letters.

Credit: Imran Mahboob/NTT Basic Research Laboratories via Physics, Wired