An acronym for Light Amplification by Stimulated Emission of Radiation. A device that uses stimulated emissions to produce a coherent beam of electromagnetic radiation.

A device for producing light by emission of energy stored in a molecular or atomic system when stimulated by an input signal. It has a cavity, with mirrors at the ends, filled with material such as crystal, glass, liquid, gas or dye. It produces an intense beam of light with the unique properties of coherency, collimation and monochromaticity.

Common types of lasers include solid state (glass or cystalline bulk material), semiconductor (based on p-n junctions), and gas lasers. Fibre lasers are doped glass lasers designed to amplify the light in optical fibres.

Class IGenerally exempt from radiation hazard controls during operation. Typically emit continuous wave at less than 0.4µW at visible wavelengths.
Class IILow power visible lasers which emit above Class I levels but emitting a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
Class IIABased upon a 1000 second exposure and applies only to lasers that are "not intended for viewing" such as a supermarket laser scanner. The upper power limit of Class IIA is 4.0 micro-Watts. These are products whose emission does not exceed the Class I limit for an emission duration of 1000 seconds.
Class IIIAIntermediate power lasers (contiuous wave 1-5 mW). Only hazardous for intrabeam viewing. Some limited controls are usually recommended.
Class IIIBModerate power lasers (continuous wave 5-500 mW, pulsed: 10 J/cm2 - or the diffuse reflection limit, which ever is lower). In general, Class IIIB lasers will not be a fire hazard and are not generally capable of producing a hazardous diffuse reflection except for conditions of intentional staring done at distances close to the diffuser. Specific controls are recommended.
Class IVHigh power lasers (continuous wave 500 mW) are hazardous to view under any condition (directly or diffusely scattered) and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.

Most lasers used in fibre optic communications are solid-state semiconductor devices.

See also: Accessible Emission Level, Axial Flow Laser, Carbon Dioxide Laser, Gas Laser, Helium-Neon Laser, HeNe Laser, Infrared Amplification by Stimulated Emission of Radiation, Ion Laser, laser Cooling, Laser Diode, Neodymium Yttrium Aluminum Garnet Laser, Optical Cavity, Optical Pumping, Q-Switch, Q-Switched Laser, Stimulated Emission, Transverse Electromagnetic Mode, Tunable Dye Laser, Tunable Laser, Yttrium Aluminium Garnet.

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Subjects: Optics Physics

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