Turning On The Tunable Laser

When Chung L. Tang, an electrical engineering professor at Cornell University, heard about a new optical crystal that had been developed in China in 1985, he quickly realized it was the key to building a so-called tunable laser. Unlike most lasers, which can emit only a single wavelength of light, these devices could be tuned, by turning a dial, to give off light over a broad range of wavelengths from ultraviolet to infrared.

To build such a versatile, broad-spectrum laser, Tang took advantage of an unusual property of the new beta barium borate (BBO) crystal. It splits a photon, or particle of light, in two. The wavelength of the resulting light beam depends on the angle at which the light entered the crystal. So, by simply rotating the crystal's slanted surface, the wavelength of the laser beam can be changed. Surgeons, for example, use one frequency for fusing muscle tissue and another for cauterizing blood vessels.

Tang's group spent six years developing methods for growing these BBO crystals. Cornell then licensed the technology to Spectra-Physics Lasers Inc. in Mountain View, Calif., which recently unveiled the first commercial broad-spectrum tunable lasers. The company is marketing the devices for materials processing, medical equipment, pollution monitoring, and other applications.

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