Laser-based sensor for pollution

Citation

(1998), "Laser-based sensor for pollution", Sensor Review, Vol. 18 No. 2. https://doi.org/10.1108/sr.1998.08718baf.004

Laser-based sensor for pollution

Laser-based sensor for pollution

Keywords Bell Laboratories, Lasers, Pollution, Sensors

Bell Laboratories, Murray Hill, New Jersey, scientists have demonstrated a laser-based semiconductor sensor that operates at room temperature and at high power to detect minute amounts ­ 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 chemistry. The invisible but telltale fingerprints can be detected by focusing the sensor on an area and precisely tuning the laser's wavelength until its light is absorbed.

Alastair Glass, director of the Bell Laboratories Photonics Research Laboratory, notes that the tuning range and peak power of these prototype laser sensors are "unprecedented for mid-infrared semiconductor lasers ­ about 10 and 100 times better respectively, than commercial lasers of this type ­ all of which must be cooled".

The sensor is based on the quantum-cascade (QC) laser invented at Bell Laboratories 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.

Using the sensor to detect pollutants involves scanning the area over a smokestack, for example, and changing the laser's wavelength until the light crossing the smokestack hits the pollutant's "fingerprint" and is affected by it. "This work opens up an entire field of uncooled, tunable mid and far-infrared laser sensors", says L.N. Durvasula, programme manager, Defence Sciences Office, US Defence Advanced Research Projects Agency, which partly funded the work. "This is a revolutionary development for sensor applications."

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-disc players.