Laser, LAY zuhr, is a device that produces a very narrow, powerful beam of light. Some beams are thin enough to drill 200 holes on a spot as tiny as the head of a pin. The ability to focus laser light so precisely makes it extremely powerful. For example, some beams can pierce a diamond, the hardest natural substance. Others can trigger a small nuclear reaction. A laser beam also can be transmitted over long distances with no loss of power. Some beams have reached the moon.

The special qualities of laser light make it ideal for a variety of applications. Some types of lasers, for example, are 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. Still other lasers are used to align walls and ceilings in a building or to print documents. Some lasers even 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.

At first, lasers had few uses, and scientists often thought of them as "a solution looking for a problem." Today, however, lasers rank among the most versatile and important tools in modern life.

Excerpt from the "Laser" article, The World Book Encyclopedia © 1999