Quantum Cascade Laser in Atmospheric Trace Gas Analysis

A key issue in ecosystem research and atmospheric studies is to detect and quantify low and ultra low concentrations of toxic trace gases. There has been an increasing concern about pollution of our living environment. Emission of a gas into the atmosphere usually dilutes rapidly and even at low levels of concentration, adverse effects can be noticed. The exact measurement of such low concentrations of atmosphere species poses a challenge to science and technology. When we take a ‘sample’ of the gas emission, the gas is extracted from a particular point and it is preconditioned. The method usually adopted is the ‘wet chemistry’ method. There are other methods in use, such as, gas chromatography, mass spectrometry, elemental analysis, etc. These methods require that the gas samples be preconditioned before using it for analysis. Also, these methods are slow. Optical spectroscopic techniques work without the need for preconditioning of the gas sample. They can be used for real-time measurement and ‘in-situ’ analysis. In industrial applications, monitoring gases like oxygen/ozone, carbon monoxide, ammonium hydrochloride and hydrogen fluoride are routinely carried out. A laser based gas monitor provides continuous measurement with a fast response and high sensitivity of the order of a few seconds.