HOW A LASER WORKS

Electrons travel in orbits around the nucleus of an atom. If an electron becomes excited by light, it will move to an orbit that exists at a point higher and wider than the original orbit. This orbit is not the natural habitat of the electron and at some point the electron will jump back down to its original orbit. The photon that is emitted when the electron jumps down is called spontaneous emission. This will continue until all the electrons relax to their natural state.

The same thing happens when a laser is created, only on a larger scale. To create a laser there must be a lot of atoms for the light to pass through, so the emitted light can build to high levels. The photon emitted from the first excited atom causes the excited electrons in other atoms to relax immediately to their natural state and emit additional photons traveling in the same direction. This is called stimulated emission. Because this process must grow from a low level to a higher level (more than a billion times higher), scientists place slightly curved mirrors on both ends of the matter the light is traveling through. This causes the beam of light to bounce back and forth between the mirrors, thus enhancing the amount of light given off. One of the curved mirrors is 100 percent reflective, the other is 95 percent reflective. That five percent that is not reflective allows five percent of the light to leak out of the matter. The light that leaks out is the laser beam.

This fascinating process, however, has its problems. In order to create the power beam needed by industry, extreme excitation levels must be used. Only a small amount of energy is actually used; the rest of the energy is left inside the material. This causes a lot of heat and energy problems for the technicians running the laser.

The Free Electron Laser is different from a regular laser in that it uses very fast moving electrons, which if directed around a bend, will spontaneously produce light. In order to bend the electron beam repeatedly, a device called a "wiggler" is used. The "wiggler" is a succession of magnetic fields, of alternating polarity, that are spaced at an equal distance from each other. As the beam passes through the "wiggler," the electron's path is bent by the magnetic field. Because the magnets are positioned in alternate polarity, as one point on the electron beam bends down, another point bends up. This creates the wiggle or wave effect, which causes photons to be emitted. Stimulated emission is achieved, but this time the excess heat and energy exit at the speed of light.

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Updated January 20, 2004