welding Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm)<unk> sA<unk>  is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word<unk> " is an acronym for "light amplification by stimulated emission of radiation". The first<unk>  was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A<unk>  differs from other sources of light in that it emits light which is coherent. Spatial coherence allows a<unk>  to be focused to a tight spot, enabling applications such as<unk>  cutting and lithography. Spatial coherence also allows a<unk>  beam to stay narrow over great distances (collimation), enabling applications such as<unk>  pointers and lidar.<unk> s can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond.<unk> s are used in optical disc drives,<unk>  printers, barcode scanners, DNA sequencing instruments, fiber-optic, semiconducting chip manufacturing (photolithography), and free-space optical communication,<unk>  surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in<unk>  lighting displays for entertainment. Semiconductor<unk> s 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. This permits a much smaller emitting area due to the much greater radiance of a<unk>  and avoids the droop suffered by LEDs; such devices are already used in some car headlamps.
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