HOW LASERS WORK: "Laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. It describes any device that creates and amplifies a narrow, focused beam of light whose photons are all traveling in the same direction, rather than emitting every which way at once. Lasers can be configured to emit many different colors in the spectrum, but each laser can emit only that one color. There are many different types of laser, but all of them have an empty cavity containing a lasing medium: either a crystal like ruby or garnet, or a gas or liquid. There are two mirrors on either end of the cavity, one of which is half-silvered, meaning that it will reflect some light and let some light through. In a laser, the atoms or molecules of the lasing medium are "pumped" by applying intense flashes of light or electricity. The end result is a sudden burst of so-called "coherent" light as all the atoms discharge in a rapid chain reaction.