Laser, LAY zuhr, is a device that produces a very powerful beam of light. Such a beam can travel over long distances or be focused to an extremely small diameter. Some tightly focused beams can drill 200 holes on a spot as tiny as the head of a pin. Some beams are powerful enough to pierce a diamond, the hardest natural substance. A large laser system can trigger a small nuclear reaction. Laser beams have reached the moon and been reflected back to Earth.
The special qualities of laser light make it ideal for a variety of applications. It can be used to play music, read price codes, cut and weld metal, and transmit information. Lasers can also guide a missile to a target, repair damaged eyes, and produce spectacular displays of light. Other lasers are used to align walls and ceilings in a building or to print documents. Some can detect the slightest movement of a continent.
Lasers vary greatly in size. One is almost as long as a football field. Another type is as small as a grain of salt.
A typical laser has three main parts. These parts are (1) an energy source, (2) a substance called an active medium, and (3) an optical cavity, a structure enclosing the active medium. The energy source supplies an electric current, light, or other form of energy. The atoms of the active medium can absorb the energy, store it for a while, and release it as light. Some of this light triggers other atoms to release their energy. Mirrors at the ends of the optical cavity reflect the light back into the active medium. The reflected light causes more atoms to give off light. The light grows stronger, and part of it emerges from the laser as a narrow beam. Beams can be produced with visible or invisible forms of radiation.
There are many kinds of lasers. They include solid-state lasers, semiconductor lasers, gas lasers, and dye lasers.
In 1960, the American physicist Theodore H. Maiman built the first laser. Today, lasers rank among the most versatile and important tools in modern life.
