Experiment using a (likely argon) laser. (US military)

Principal components:1. Active laser medium2. Laser pumping energy3. High reflector4. Output coupler5. Laser beam

A helium-neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. The glowing ray in the middle is an electric discharge producing light in much the same way as a neon light; though it is the gain medium through which the laser passes, it is not the laser beam itself which is visible there. The laser beam crosses the air and marks a red point on the screen to the right.

A dye laser used at the Starfire Optical Range for LIDAR and laser guide star experiments is tuned to the sodium D line and used to excite sodium atoms in the upper atmosphere.

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Laser Systems

A LASER (acronym for Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. The term has since entered the English language as a standard word, laser, losing the capitalization in the process. more...

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The back-formed verb lase means "to produce laser light" or "to apply laser light to".

In analogy with optical lasers, a device which produces any particles or electromagnetic radiation in a coherent state is also called a "laser", usually with indication of type of particle as prefix (for example, atom laser.) In most cases, "laser" refers to a source of coherent photons, i.e. light or other electromagnetic radiation.

Laser light is typically near-monochromatic, i.e., consisting of a single wavelength or color, and emitted in a narrow beam. This contrasts with common light sources, such as the incandescent light bulb, which emit incoherent photons in almost all directions, usually over a wide spectrum of wavelengths.

Laser action is explained by the theories of quantum mechanics and thermodynamics. Many materials have been found to have the required characteristics to form the laser gain medium needed to power a laser, and these have led to the invention of many types of lasers with different characteristics suitable for different applications.

The laser was proposed as a variation of the maser principle in the late 1950s, and the first laser was demonstrated in 1960. Since that time, laser manufacture has become a multi-billion dollar industry, and the laser has found applications in fields including science, the defense industry, industry, medicine, and consumer electronics.

For lasers in fiction, see also raygun.

Physics

See also: Laser science and Laser construction

A laser is composed of an active laser medium, or gain medium, and a resonant optical cavity. The gain medium transfers external energy into the laser beam. It is a material of controlled purity, size, and shape, which amplifies the beam by the quantum mechanical process of stimulated emission, discovered by Albert Einstein while researching the photoelectric effect. The gain medium is energized, or pumped, by an external energy source. Examples of pump sources include electricity and light, for example from a flash lamp or from another laser. The pump energy is absorbed by the laser medium, placing some of its particles into high-energy ("excited") quantum states. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this condition, an optical beam passing through the medium produces more stimulated emission than the stimulated absorption, so the beam is amplified. An excited laser medium can also function as an optical amplifier.