Hail the first sound 'lasers'
Sometimes called "sasers", one of the devices emits sound at about 400 GHz while the other operates in the megahertz range. The differences between the two devices suggest that sasers could be made to operate over a wide range of frequencies.
Very high frequency sound could be used to probe the interiors of tiny objects – and the ability to create laser-like beams of sound could lead to new imaging applications.
Just as light behaves as both particle and wave, sound can be described in terms of particles called phonons – quanta of vibrational energy that behave in much the same way as photons.
At the heart of any optical laser is a medium with an electronic transition that involves the emission of a photon. The medium is "pumped" by an external energy source so that the majority of the electrons are in the higher energy state of the transition. When such a state decays, it emits a photon that can stimulate the emission of many more photons – which in turn stimulate further emission. Because they are all produced by the same quantum process, the photons emerge as a coherent beam of light
To read full article. Source: http://physicsworld.com/cws/article/news/41857
