Trace Gas Detection System Based on Photoacoustic and Photothermal Spectroscopy Using Ring Fiber Laser and Quartz Tuning Fork

Abstract

In this paper, a dual-spectroscopy gas sensing system based on ring cavity laser and quartz tuning fork (QTF) is designed. 15 m erbium-doped fiber with 1500 ppm doping concentration is used as gain medium, piezoelectric transducer (PZT) and acousto-optic modulator (AOM) are used as detection method. The first fiber collimator (FC) emits laser beam, laser is received by the second FC after passing through an off-beam acoustic micro-resonator (AmR) for quartz-enhanced photoacoustic spectroscopy (QEPAS) signal excitation and enhancement. The received laser is transmitted through the optical fiber and then incident on the QTF prongs by the third FC, which excites and quartz-enhan-ced photothermal spectroscopy (QEPTS) signal. Combined with the ring intra-cavity fiber laser and wavelength scanning and intensity modulation technology, dual-spectroscopy gas detection is realized. Compared with the single detection of QEPAS or QEPTS signals, the detection limit is enhanced. Under the conditions of 400mW pump power and 2500 ppmv acetylene (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> ) gas concentration, the signal to noise ratio (SNR) of QEPAS, QEPTS and dual-spectroscopy signals are 838.07, 1117.47 and 2096.26, respectively, and the minimum detection limits (MDL) of 2.98 ppmv, 2.24 ppmv, 1.19 ppmv are achieved, respectively.