Lasers are characterized according to their wavelength in a vacuum. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length) along the beam. Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have a very low divergence to concentrate their power at a great distance. Spatial (or transverse) coherence is typically expressed through the output being a narrow beam, which is diffraction-limited. Lasers are distinguished from other light sources by their coherence. This permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs such devices are already used in some car headlamps. Semiconductor lasers in the blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source.
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Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic, and free-space optical communication, semiconducting chip manufacturing ( photolithography), 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. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum.
Spatial coherence also allows a laser beam to stay narrow over great distances ( collimation), enabling applications such as laser pointers and lidar (light detection and ranging). Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Ī laser differs from other sources of light in that it emits light that is coherent. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation. A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
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