Acronym for Light Amplification by Stimulated Emission of
Radiation, device for the creation and amplification of a narrow, intense beam
of coherent Light. In a laser, the Atoms or Molecules of a Crystal, such as ruby or garnet - or of a Gas, li
quid (see States Of Matter), or other substance - are excited so that more of them are at higher Energy levels than are at lower energy levels. If a Photon(s)
whose Frequency corresponds to the energy difference between the excited and ground states
strikes an excited atom, the atom is stimulated, as it falls back to a lower
energy state, to emit a second photon of the same (or a proportional) frequency, in
phase with (see Wave) and in the same direction as the bombarding photon. This process is called
stimulated emission. The bombarding photon and the emitted photon may then each
strike other excited atoms, stimulating further emission of photons, all of the
same frequency and phase. This process produces a sudden burst of coherent Radiation as all the atoms discharge in a rapid chain reaction. First built in 1960,
lasers now range in size from Semiconductor lasers as small as a grain of salt (see Sodium Chloride) to solid-state and gas lasers as large as a building. The light beam
produced by most lasers is pencil-thin and maintains its size and direction over very
large distances. Lasers are widely used in industry (for cutting and boring
metals and other materials), in medicine (for self-cauterizing surgery), and in Communications, scientific research, and Holography. They are an integral part of such familia
r devices as bar-code scanners,
laser printers, and Compact Disk (CD) players.