MURRAY HILL, N.J., Oct. 27 -- Bell Labs has unveiled what it calls the world's first bi-directional semiconductor laser. According to researchers at Bell Labs, the R&D division of Lucent Technologies, the device emits light at two widely different wavelengths depending on the direction of electrical current flowing through it. In conventional semiconductor lasers, current can flow only in one direction. The new laser was designed by Claire Gmachl, a researcher with Bell Labs' Semiconductor Physics Research Department. It's a radically new concept, noted Federico Capasso, head of the department and a member of the research team. This is one laser that behaves as if it were two, emitting light at different wavelengths depending on whether the applied voltage is negative or positive. The prototype laser emits light in the invisible region of the spectrum, where most gases and vapors have telltale light-absorption fingerprints, which could make the device useful in such applications as the detection of atmospheric pollution. Varying the wavelength of the laser pulses from being in resonance with the fingerprint of a gas to being out of resonance would change the intensity of light arriving at a detector. The detector could measure these changes to determine the concentration of the atmospheric pollutant.