Methane CH4 concentration measurements in the mid-infrared range utilizing a TDLS spectrometer calibration relation

The simulation approach of TDLS has been proven in this study to improve spectrometer sensitivity by modifying the wavelength of a DFB tunable laser diode using a sinusoid signal. Because the laser's driving current has been set, the wavelength of the laser diode will shift in tuning limits to around 0.02 nm in the Mid Infrared Area (MIR) region for a poisonous gas Methane CH4.

The sensitivity of TDLS was tested at a constant concentration of 0.5ppb and a constant length of the open path (the distance between the laser source and the retroreflector) of 100m. After writing a MATLAB algorithm to set the correct wavelength in the MIR region, frequency domain measurements were performed to extract the second harmonic as an indication of gas presence. The precise wave length of methane gas in the MIR area is (3290.987nm). It should be noted that for all gas types measured at L = 100 m, the gas concentration ranged from N = 0.05 to 0.5 ppm in 0.2 steps.