Rapid detection of methane, carbon dioxide and ammonia for harsh environments using tunable doide laser spectroscopy

This paper reports time-varying and simultaneous detection of the pressure and concentration, of hazardous gases such as methane, carbon dioxide and ammonia using tunable diode laser spectroscopy (TDLS). The concentration and pressure of the gases is extracted with a time resolution of 10s, which makes this method useful in applications that require in situ, real-time measurements of several gases. A calibration-free wavelength modulation spectroscopy (WMS) approach known as the Residual Amplitude Modulation (RAM) method has been used at a modulation frequency when intensity modulation (IM) is at phase-quadrature to the frequency modulation (FM). TDLS offers the dual advantage of remote detection of gases and quantification of gas parameters. This makes them ideally suited to hazardous environments such as coal mines.