Laser

A laser is an optical source that emits photons in a coherent beam.
Laser light is typically near-monochromatic, consisting of a very small band of wave-lengths or a very specific color, and emitts in a narrow beam.
Many materials have been found to have the required characteristics to form the laser gain medium needed to power a laser, and these have led to the invention of many types of lasers with different characteristics suitable for different applications.
The laser was proposed as a variation of the maser principle in the late 1950s, and the first laser was demonstrated in July 1960 by Theodore Maiman at Hughes Research Laboratories. Since that time, laser manufacture has become a multi-billion dollar industry, and the laser has found applications in fields including science, the defense industry, medicine, and consumer electronics.
The light generated by stimulated emission is very similar to the input signal in terms of wave-length, phase, and polarization. This gives laser light its characteristic coherence. A beam generated by a small laboratory laser such as a helium-neon laser spreads to about 1.6 kilometers (1 mile) diameter. However, such a divergent beam can be transformed into a collimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well or much.