| 单词 | laser (light amplification by stimulated emission of radiation) |
| 释义 | laser (light amplification by stimulated emission of radiation) A device that produces an intense, coherent, collimated, focused, and nearly monochromatic beam of radiated optical energy by stimulating electronic, ionic, or molecular transitions to lower energy levels. A laser comprises an active medium, or gain medium, and a resonant cavity. An external power source, or pump, in the form of electricity or another laser, energizes the gain medium, which absorbs the energy. Some of the particles in the gain medium are excited into quantum high-energy states. When a critical level of energy is achieved, a light signal passing through the medium produces more optical energy than is absorbed, and the signal is greatly amplified.The resulting radiated optical signal is highly coherent, i.e., consistent in phase and polarization, and virtually monochromatic.Through a resonating cavity and either mirrors or a diffraction grating, the signal is narrowly channeled and collimated, i.e., the rays are lined up so that they are virtually parallel. Fiber optic transmission systems (FOTS) in long haul applications employ semiconductor diode lasers, generally Fabry-Perot lasers or distributed feedback (DFB) lasers. Short haul transmission systems such as those associated with local area networks (LANs) more commonly employ light-emitting diodes (LEDs) or vertical cavity surface-emitting lasers (VCSELs) as light sources. ( Note: The laser was patented by AT&T Bell Telephones in 1960 as the optical maser.) See also coherence, collimation, DFB laser, Fabry-Perot laser, LED, maser, pump laser, radiation, and VCSEL. |
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