The laser based gas detection employs a basic fact that gases absorb optical radiation at unique wavelengths. These spectral gas absorption lines are very narrow and sharp. If a laser radiating at a central wavelength close to the absorption line of a gas is modulated such that its output wavelength is scanned across the absorption line of the gas, then in the presence of the gas the laser radiation is proportionally absorbed. A detector measuring the laser output measures reduced intensity every time the laser output wavelength coincides with that of gas absorption line. If the laser is modulated at a frequency f, the laser wavelength scans across the gas absorption line twice in each cycle; thus the gas detection information is available at 2f frequency. The amplitude of the absorption signal is proportional to the level gas distribution through which the laser light passes before being detected by the detector. Using lasers with different gas specific wavelengths, several different gas detectors can be bundled together (e.g methane, carbon dioxide, oxygen, hydrogen etc). A short haul wireless methane monitoring and the concentration mapping system is presented as one of the wireless systems. >
Examples of other chemical systems include:
