Sasers: Sound-based Lasers Invented

You've heard of lasers. They're focused beams of light used in everything from supermarket scanners to DVD players and futuristic weapons.

Now scientists have created what they call a "saser," the sound-based equivalent.

A saser produces an intense beam of uniform sound waves on a nano scale, scientists say. The new device could have significant and useful applications in the worlds of computing, imaging and even anti-terrorist security screening.

"While our work on sasers is driven mostly by pure scientific curiosity, we feel that the technology has the potential to transform the area of acoustics, much as the laser has transformed optics in the 50 years since its invention," said professor Anthony Kent from the University of Nottingham School of Physics and Astronomy.

The breakthrough, announced today, is detailed in this month's issue of the journal Physical Review B. Sasers had, until now, only been a theoretical concept.

"Laser" stands for Light Amplification by the Stimulated Emission of Radiation. Albert Einstein laid the theoretical groundwork in 1917 for the invention of lasers, but the first working laser device wasn't created until 1960.

A laser uses packets of electromagnetic vibrations called photons, the units of all light in the electromagnetic spectrum, including visible, infrared and X-rays.

A saser uses sound waves composed of sonic vibrations called phonons.

In a laser, the photon beam is produced by stimulating electrons with an external power source so they release energy when they collide with other photons in a highly reflective optical cavity, the researchers explain. This produces a coherent and controllable shining beam of laser light in which all the photons have the same frequency and rate of oscillation.

The saser mimics this technology, but using sound, to produce a sonic beam of phonons. The beam travels, not through an optical cavity like a laser, but through a tiny man-made structure called a superlattice. This is made out of around 50 super-thin sheets of two alternating semiconductor materials, gallium arsenide and aluminium arsenide, with each layer just a few atoms thick.

When stimulated by a power source (a light beam), the phonons multiply, bouncing back and forth between the layers of the lattice, until they escape out of the structure in the form of an ultra-high frequency phonon beam.

A key factor in this new science is that the saser is the first device to emit sound waves in the terahertz frequency range, the researchers said. The beam of coherent acoustic waves it produces has nanometer wavelengths (billionths of a meter).

Terahertz radiation is also used to reveal what's under your clothes in airport scans.

In the future, a saser might spot defects in nanometer-scale objects like micro-electric circuits. Or sasers might be used for medical imaging and security screening in novel ways.

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