How lasers work

McClatchy NewspapersDecember 9, 2009 

WASHINGTON — A laser is a device that creates an intense beam of light and focuses it tightly in one direction. The difference between regular light and laser light is like the difference between a water sprinkler and a fire hose.

The name stands for "light amplification by stimulated emission of radiation."

Laser light differs from ordinary light because its photons — tiny packets of light energy — are all of the same wavelength and color, and they march in lockstep in the same direction. In contrast, photons in ordinary light scatter every which way.

Laser light is created by a bright flash of ordinary light aimed at a tube of special glass, crystal or gas. The flash pumps extra energy into the tube. That energy "excites'' the electrons that are orbiting the nuclei of the atoms in the tube. An excited electron moves up to a higher orbit, then relaxes and drops back to a lower, less energetic orbit. In the process, it emits a photon.

A system of mirrors rapidly bounces the photons back and forth in the laser tube. Photons from one atom stimulate photons from other atoms, amplifying the intensity of the light. The result is a straight, bright beam of laser light.

Lasers can be "tuned'' to produce beams of different colors and intensities. Early lasers produced about 10,000 watts. The lasers at the Department of Energy's National Ignition Facility generate trillions of watts.

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