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system producing four orange laser guide stars |alt=A telescope emitting four orange laser beams A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word laser originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow and the optical amplifier patented by Gordon Gould. A laser differs from other sources of light in that it emits light that is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling uses such as optical communication, laser cutting, and lithography. It also allows a laser beam to stay narrow over great distances (collimation), used in laser pointers, lidar, and free-space optical communication. Lasers can also have high temporal coherence, which permits them to emit light with a very narrow frequency spectrum. Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations measured in attoseconds.…

system producing four orange laser guide stars |alt=A telescope emitting four orange laser beams A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word laser originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow and the optical amplifier patented by Gordon Gould. A laser differs from other sources of light in that it emits light that is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling uses such as optical communication, laser cutting, and lithography. It also allows a laser beam to stay narrow over great distances (collimation), used in laser pointers, lidar, and free-space optical communication. Lasers can also have high temporal coherence, which permits them to emit light with a very narrow frequency spectrum. Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations measured in attoseconds. Lasers are used in fiber-optic and free-space optical communications, optical disc drives, laser printers, barcode scanners, semiconductor chip manufacturing (photolithography, etching), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. The laser is regarded as one of the greatest inventions of the 20th century. N_b(\rho(\nu,T)B_{ba} + A_{ba}) = N_a \rho(\nu,T)B_{ab} If a powerful auxiliary source excites the atoms to the higher state, then N_a \rightarrow 0 and the equilibrium will be broken. This is called population inversion. Some of the N_b atoms will spontaneously emit light and others will respond with stimulated emission creating an avalanche of photons in phase. == Field of study == Laser science or laser physics studies lasers, both through theory and practice. Laser science is principally concerned with quantum electronics, laser construction, optical cavity design, the physics of producing a population inversion in laser media, and the temporal evolution of the light field in the laser. It is also concerned with the physics of laser beam propagation, particularly the physics of Gaussian beams, with laser applications, and with associated fields such as nonlinear optics and quantum optics. Northrop Grumman's Press Release on the Firestrike 15 kW tactical laser product Website on Lasers 50th anniversary by APS, OSA, SPIE Advancing the Laser anniversary site by SPIE: Video interviews, open-access articles, posters, DVDs Bright Idea: The First Lasers history of the invention, with audio interview clips. Free software for Simulation of random laser dynamics Video Demonstrations in Lasers and Optics Produced by the Massachusetts Institute of Technology (MIT). Real-time effects are demonstrated in a way that would be difficult to see in a classroom setting. MIT Video Lecture: Understanding Lasers and Fiberoptics Virtual Museum of Laser History, from the touring exhibit by SPIE website with animations, applications and research about laser and other quantum based phenomena Université Paris Sud

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