Abstract
An evanescent-wave quartz-enhanced photoacoustic spectroscopy (EW-QEPAS) CO sensor was developed using a tapered fiber integrated with the quartz tuning fork (QTF) and micro-resonator (mR) tubes. The fiber taper was inserted through the two mR tubes with the taper waist located between the QTF prongs. A fiber-coupled continuous-wave distributed feedback (DFB) laser at 2.3μm was connected with the fiber taper fabricated by the flame-brushing method. The fiber taper has negligible influence on the resonant frequency and Q-factor of the QTF, but significantly reduces the background noise compared with the recently developed fiber tip-based EW-QEPAS sensor. In the EW-QEPAS detection with wavelength modulation spectroscopy, we investigated the optimal modulation depth and gas pressure, which are different from that of the conventional free-space QEPAS detection. The current CO sensor achieved a minimum detection limit of ∼20ppm at the 210-s averaging time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 1.44×10−8cm−1W/√Hz.
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