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

Abstract

Quartz-enhanced 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 f 0 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 µm and an interband cascade laser (ICL) with a center wavelength of 4.47 µm were used as the light sources to simultaneously irradiate on different surfaces of QTF for scanning the absorption lines of carbon dioxide (CO 2 ) and nitrous oxide (N 2 O). A multi-pass cell with an effective optical path of 40 m and a 40 cm absorption cell were selected for the measurements of CO 2 and NO 2 , respectively. The developed sensor was validated by the detection of mixtures containing 3000 ppm CO 2 and 20 ppm N 2 O. The relationships between the second harmonic (2f) amplitude of the QEPTS signal and the CO 2 and N 2 O 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 CO 2 in an integration time of 195 s and 0.038 ppb for N 2 O in an integration time of 90 s, respectively.

In Situ All-Fiber Remote Gas Sensing Strategy Based on Anti-Resonant Hollow-Core Fiber and Middle-Hole Eccentric-Core Fiber

“…Laser absorption spectroscopy has become a powerful tool for gas detection in atmospheric sciences, industrial safety and protection, leakage identification, and many other applications because of the exceptional selectivity and sensitivity in the infrared spectral region [1][2][3]. With the development of semiconductor lasers, narrow linewidth lasers can operate at specific wavelengths by adjusting the injection current or operating temperature, and accurate measurements can be achieved by scanning the absorption lines of the gas [4].…”