Quantitative wavelength modulation spectroscopy for gas measurements - Elimination of laser intensity modulation effects

Quantitative tunable diode laser spectroscopy (TDLS) has established itself as a very powerful technique for the detection of gases in field applications such as industrial process control. Recent calibration-free techniques have made field measurements more robust. However, in many situations, the significant levels of laser intensity modulation gives rise to background signals that either limit detection sensitivity or distort the target signals, thereby making it difficult to extract useful information. This paper outlines the recent trends in calibration-free wavelength modulation spectroscopy (WMS) and focuses on the elimination of the undesirable effects of both linear as well as nonlinear intensity modulation. The approach is generic and should be useful with newer types of lasers that have shown significantly nonlinear power-current characteristics. © 2011 SPIE.