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Laser An acronym for Light Amplification by Stimulated Emission of Radiation. A device that uses stimulated emissions to produce a coherent beam of electromagnetic radiation. 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 | Criteria | | Class I | Generally exempt from radiation hazard controls during operation. Typically emit continuous wave at less than 0.4µW at visible wavelengths. | | Class II | Low 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 IIA | Based 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 IIIA | Intermediate power lasers (contiuous wave 1-5 mW). Only hazardous for intrabeam viewing. Some limited controls are usually recommended. | | Class IIIB | Moderate 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 IV | High 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, Laser Diode, Optical Cavity, Optical Pumping, Stimulated Emission, Yttrium Aluminium Garnet.
  
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