Pptv-Level Intra-Cavity QEPAS Sensor for Acetylene Detection Using a High Power Q-Switched Fiber Laser

Abstract

A high-sensitivity quartz enhanced photoacoustic spectroscopy (QEPAS) system based on acousto-optic Q-switched fiber laser for C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detection was proposed and experimentally demonstrated. The gas sensor system coupled an erbium-doped fiber laser with a custom-made transmission quartz tuning fork structure. An acousto-optic modulator was used to perform amplitude modulation at a modulation frequency of 32.76 kHz and the system achieved a maximum intra-cavity peak pulse power of 6 W. The system response relationship between the peak pulse power and QEPAS signals confirms that saturation does not occur with the laser power less than 6 W. Preliminary measurements of the sensor response to C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations have been made with pure N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as a carrier gas, and the experimental results showed the relationship between QEPAS signal amplitude and the C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations have a good linearity (R-square = 0.99918). Finally, trace gas measurements have been assessed and a minimum detection limit of 101 pptv within 20 ms integration time for C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has been achieved. This paper provides a valuable gas sensor for practical project application.