Donna Cunningham
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Carl Blesch
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BELL LABS SCIENTISTS DEMONSTRATE NEW HIGH-POWER, LASER-BASED SENSOR TECHNOLOGY FOR GAS DETECTION, POLLUTION MONITORING
FOR IMMEDIATE RELEASE MURRAY HILL, N.J. æ In a major breakthrough, Bell Labs scientists have demonstrated the worldÃs first laser-based semiconductor sensor that operates at room temperature and at high power to detect minute amounts ñ potentially parts per billion -- of trace gases or pollutants by scanning for their optical-absorption "fingerprints." Gases or pollutants are identifiable by their absorption wavelengths, which depend on their chemical nature. The invisible but telltale fingerprints can be detected by focusing the sensor on an area and precisely tuning the laserÃs wavelength until its light is absorbed.
"This is a major accomplishment," said Alastair Glass, director of the Bell Labs Photonics Research Laboratory. "The tuning range and peak power of these prototype laser sensors are unprecedented for mid-infrared semiconductor lasers ñ about 10 and 100 times better, respectively, than commercial lasers of this type ñ all of which must be cooled."
The experimental sensor is based on the novel quantum-cascade (QC) laser invented at Bell Labs just three years ago and demonstrated at room temperature operation last year. The newest versions can be continuously tuned to operate at any of a wide range of single frequencies in the mid-infrared region of the electromagnetic spectrum, the region in which light is invisible and causes heat.
The laserÃs wavelength is determined by several factors. In manufacture, varying the thicknesses of the material layers of the laser sets its wavelength, and adding a grating (etched material) on top of the laser makes the wavelength more precise. In use, adjusting the temperature or the electrical current applied to the laser changes its wavelength.
Using the sensor to detect pollutants involves scanning the area over a smokestack, for example, and shifting the laserÃs wavelength until the light crossing the smokestack hits the pollutantÃs "fingerprint" and is affected by it.
"This work opens up an entire field of uncooled, tunable mid- and far-infrared laser sensors," said L.N. Durvasula, program manager, Defense Sciences Office, U.S. Defense Advanced Research Projects Agency (DARPA), which partly funded the work. "This is a revolutionary development for sensor applications."
The Bell Labs research team includes Jerome Faist, Claire Gmachl, Federico Capasso, Carlo Sirtori, Deborah Sivco, James Baillargeon and Alfred Cho, in collaboration with Professor Edward Whittaker of the Stevens Institute of Technology in Hoboken, N.J.
"WeÃre happy to have moved very quickly from basic research to practical application," said Federico Capasso, head of the Quantum Phenomena and Device Research department. "The enabling technology behind all this is the marriage of optics, quantum physics, and crystal growth, in the QC laser, and we foresee a number of market opportunities for these portable, robust devices." Potential environmental applications include pollution monitoring, automotive emission sensing and combustion diagnostics; law-enforcement possibilities, such as the detection of explosives or of fugitive emissions from illicit drug-manufacturing sites; military applications like portable battlefield sensing of toxic gases and biological toxins; as well as industrial process control, collision-avoidance radar and medical applications. Conventional semiconductor lasers, which operate at wavelengths from near-infrared to visible, are widely used in other applications such as lightwave communications and compact-disk players. Detailed information about the distributed-feedback QC laser sensor appears in this weekÃs issue of the journal Applied Physics Letters. Gmachl will present the research teamÃs latest experimental results in a post-deadline talk on Thursday at the joint Conference on Lasers and Electro-Optics (CLEO '97) and Quantum Electronics and Laser Science Conference (QELS '97) in Baltimore. Lucent Technologies designs, builds and delivers a wide range of public and private networks, communications systems and software, consumer and business telephone systems and microelectronics components. Bell Labs is the research and development arm for the company. Further information about the company is available at http://www.lucent.com. -###-
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