Laser

A laser (light amplification by stimulated emission of radiation) is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

In stimulated emission, first considered by Albert Einstein in 1917, an energetic photon causes an electron to drop to a lower energy level, which results in the creation of another photon. This second photon is coherent with the first and has the same phase, frequency, polarization, and direction of travel as the first photon. If the photons are reflected so that they repeatedly traverse the same atoms, an amplification can take place and an intense radiation beam is emitted. Lasers can be created so that they emit electromagnetic radiations of various kinds, and thus there are X-ray lasers, ultraviolet lasers, infrared lasers, etc.

Theodore Maiman created the first practical working laser in 1960, using a pulsed operation that works the same as today's electronic devices.

A laser emits coherent light allowing focus to a spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, enabling laser pointers and lidar. Lasers are used in optical disc drives, laser printers, barcode scanners, fiber-optics and optical communication, laser surgery, cutting and welding materials, marking targets and measuring range and speed, laser lighting displays for entertainment, and weaponry.