Lasers

About laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
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 applications such as optical communication, laser cutting, and lithography. It also allows a laser beam to stay narrow over great distances (collimation), a feature used in applications such as 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 as short as an attosecond

Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic and free-space optical communications, 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. 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; 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.