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(Light Amplification by the Stimulated Emission of Radiation) A device that creates a uniform and coherent light that is very different from an ordinary light bulb. Many lasers deliver light in an almost-perfectly parallel beam (collimated) that is very pure, approaching a single wavelength. Laser light can be focused down to a tiny spot as small as a single wavelength.

     Laser output can be continuous or pulsed and is used in a myriad of applications. Gas lasers are used to cut steel and perform delicate eye surgery, while solid state lasers create the ultra-high-speed, minuscule pulses traveling in optical fibers traversing the backbones of all major communications networks. Light traveling in an optical fiber is impervious to external interference, a constant problem with electrical pulses in copper wire. See optical fiber.

How Does It Work?
A laser is an optical oscillator, which is made out of a solid, liquid or gas with mirrors at both ends. To make the laser work, the material is excited or "pumped," with light or electricity. The pumping excites the electrons in the atoms, causing them to jump to higher orbits, creating a "population inversion." A few of the electrons drop back to lower energy levels spontaneously, releasing a photon (quantum of light). The photons stimulate other excited electrons to emit more photons with the same energy and thus the same wavelength as the original. The light waves build in strength as they pass through the laser medium, and the mirrors at both ends keep reflecting the light back and forth creating a chain reaction and causing the laser to "lase."

     In simple laser cavities, one mirror has a small transparent area that lets the laser beam out. In semiconductor lasers, both mirrors often transmit a beam, the second one being used for monitoring purposes.




Laser Action
The combination of spontaneous emission first, and then stimulated emission, causes the laser to "lase," which means it generates a coherent beam of light at a single frequency.




Who Invented It?

In 1957, the laser was conceived by Gordon Gould, a graduate student in physics at Columbia University. When Gould filed for patents in 1959, he found that Columbia professor Charles Townes and Arthur Schawlow of Bell Labs had already filed for them. The year before, AT&T had, in fact, demonstrated a working laser at Bell Labs. In 1977, after years of litigation, a court awarded Gould rights to the first of three patents and later to all of them. He finally reaped millions in royalties.




Developing the Laser
This photo of the development of the helium-neon laser was taken at AT&T's Bell Laboratories in 1964. (Image courtesy of AT&T.)
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