Optical fiber tip-based quartz-enhanced photoacoustic sensor for trace gas detection
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We reported the development of an evanescent-wave quartz-enhanced photoacoustic sensor (EW-QEPAS) using a single-mode optical fiber tip for sensitive gas detection in the extended near-infrared region. It is a spectroscopic technique based on the combination of quartz-enhanced photoacoustic spectroscopy with fiber-optic evanescent-wave absorption to achieve low optical noise, easy optical alignment, and high compactness. Carbon monoxide (CO) detection at 2.3 μm using a fiber-coupled, continuous-wave, distributed-feedback laser was selected for the sensor demonstration. By tapering the optical fiber down to 2.5 μm diameter using the flame-brushing technique, an evanescent field of ~0.6 mW around the fiber tip was absorbed by CO molecules. Besides an excellent linear response (R 2 = 0.9996) to CO concentrations, the EW-QEPAS sensor achieved a normalized noise-equivalent absorption (NNEA) coefficient of 8.6 × 10−8 cm−1W/√Hz for an incident optical power of 1.8 mW and integration time of 1 s. The sensor detection sensitivity can be further improved by enhancing the evanescent-wave power on the fiber tip.
KeywordsHONO Evanescent Field Photoacoustic Signal Quartz Tuning Fork Incident Optical Power
This research is supported by the Early Career Scheme (ECS) grant from the Research Grants Council of the Hong Kong SAR, China (24208515); Shun Hing Institute of Advanced Engineering grant (RNE-p2-15); and CUHK Direct Grant for Research. We thank Prof. Wei Jin’s group from Hong Kong Polytechnic University for the use of their equipment.
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