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Pure Silicon Laser Debuts

Researchers from the University of California at Los Angeles have made a prototype laser from the stuff of computer chips -- silicon. The laser is tunable, meaning it can lase in a range of wavelengths, or colors, and it works at room temperature.



The silicon laser could be used to provide optical wireless communications at a wavelength that is optimal for transmission through air and even fog, to detect chemicals and biological molecules, and to provide an infrared countermeasure capable of jamming heat-seeking missiles, according to the researchers.



The device promises to be compatible with today's silicon manufacturing processes because it amplifies light using the natural atomic vibrations of silicon rather than a mix of materials or a particular nanoscale physical structure. This makes silicon lasers potentially inexpensive.



A laser, short for light amplification by stimulated emission of radiation, energizes matter. When an atom absorbs energy its electrons move to higher energy levels.



Ordinarily silicon makes a poor laser medium because when its electrons drop to a lower energy level more energy is channeled into the material as vibrations or heat than is emitted as light. The researchers got around this problem using the Raman effect.



When photons strike atoms, many are absorbed and some scatter. The scattered photons gain or lose energy depending on whether the atoms they struck are in a high or low energy state. The energy change causes the photons' wavelength to shift.



When a powerful enough laser strikes a material, the scattered photons induce lasing at the Raman-shifted wavelength. Raman lasers made from glass optical fiber are common. The researchers found that the Raman effect is 10,000 times stronger in silicon than in optical fiber.



A practical silicon Raman laser could be ready in two years. The work appeared in the October 18, 2004 issue of Optics Express.

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