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Laser Pointers Draw Attention To Themselves (NYT reg req'd)

Pretty Photons, All in a Row

Red laser pointers are so inexpensive that they are handed out as promotional novelties, but now some pointer manufacturers have introduced more expensive models that emit green light.

"The eye is so much more sensitive to green than red; the new ones look radically more bright," Mr. Baker said. "They seem a lot more dazzling."

Green laser pointers cost more - $100 or more, compared with a few dollars for a simple red pointer - because they are actually two lasers in one. A basic red laser uses a simple kind of semiconductor crystal called a diode. The electrons in the crystal are excited, or pumped, to higher energy states by electricity. When the electrons fall back to lower energy states, a photon of light is emitted. These photons in turn cause other photons to be emitted, of the same wavelength and phase and traveling in the same direction. The result is a coherent beam of light of one color.

But green laser diodes are not readily available. So a green pointer first uses a diode that produces an infrared beam. These infrared photons are used to pump a second lasing material, a crystal, which produces light of a different wavelength that is converted to green through a frequency-doubling process.


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