Lasers have become ubiquitous: they read the prices of our groceries, play our compact discs, and even clean our clogged arteries. Now, thanks to a group of French physicists, the world has its first saser- -a device that amplifies sound the way lasers amplify light. The saser isn’t of much use yet, but one day the researchers hope to turn it into the world’s most sensitive listening device.
A laser--the name stands for light amplification by stimulated emission of radiation--exploits the peculiar quantum interactions between atoms and light. An atom can absorb a photon, or light particle, by boosting one of its electrons to a higher energy, but it’s unstable in this state. Eventually it sheds another photon and returns to its calmer existence. When an already excited atom is hit by another photon, however, it can’t absorb it; instead it releases a photon of the same color, or frequency. ...
