Laser

A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical source composed of a resonant optical cavity and a gain medium.

Physics

The basic physics of lasers centres around the idea of producing a population inversion in a laser medium by "pumping" the medium; i.e., by supplying energy in the form of light or electricity, for example. The medium may then amplify light by the process of stimulated emission. If the light is circulating through the medium by means of a cavity resonator, and the gain (amplification) in the medium is stronger than the resonator losses, the power of the circulating light can rise exponentially. Eventually it will get so strong that the gain is saturated (reduced). In continuous operation, the intracavity laser power finds an equilibrium value which is saturating the gain exactly to the level of the cavity losses. If the pump power is chosen too small (below the "laser threshold"), the gain is not sufficient to overcome the resonator losses, and the laser will emit only very small light powers.

Related Topics:
Population inversion - Laser medium - Cavity resonator

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A further note on the terminology is necessary. As laser stands for light amplification by stimulated emission of radiation, it should be understood that the word light is here meant in the expansive sense, as photons of any energy; not as simply photons in the visible spectrum. Hence there are X-ray lasers, IR-lasers, UV-lasers, microwave lasers, radio lasers, etc. However, microwave lasers and radio lasers are usually called masers in the modern terminology. In addition, some argue that all lasers can be thought of as masers (see the article on maser for details).

Related Topics:
Photons - Visible spectrum - Maser

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