Simultaneous Detection of CO2 and N2O Based on Quartz-Enhanced Photothermal Spectroscopy by Using NIR and MIR Lasers

photothermal spectroscopy (QEPTS) technique is suitable for simultaneous measurement of multi-gas in near-infrared (NIR) and mid-infrared (MIR) bands with advantages of wide spectral response and high sensitivity. Here, we report a multi-gas sensing system based on QEPTS using NIR and MIR Lasers. A quartz tuning fork (QTF) with a resonant frequency f0 of 32.742 kHz was employed as a photothermal detector. A continuous wave distributed feedback (CW-DFB) fibercoupled diode laser with a center wavelength of 1.58 & mu;m and an interband cascade laser (ICL) with a center wavelength of 4.47 & mu;m were used as the light sources to simultaneously irradiate on different surfaces of QTF for scanning the absorption lines of carbon dioxide (CO2) and nitrous oxide (N2O). A multi-pass cell with an effective optical path of 40 m and a 40 cm absorption cell were selected for the measurements of CO2 and NO2, respectively. The developed sensor was validated by the detection of mixtures containing 3000 ppm CO2 and 20 ppm N2O. The relationships between the second harmonic (2f) amplitude of the QEPTS signal and the CO2 and N2O concentrations were investigated. Allan deviation analysis showed that this sensor had excellent stability and high sensitivity with a minimum detection limit (MDL) of 2.729 ppm for CO2 in an integration time of 195 s and 0.038 ppb for N2O in an integration time of 90 s, respectively.